refactor(struct): rework on type plugin system

.gitignore

@@ -1,5 +1,7 @@
-lib
+cjs
+esm
+dts
 node_modules
 *.log
-tsconfig.tsbuildinfo
+*.tsbuildinfo
 /package-lock.json

.vscode/settings.json

@@ -45,6 +45,7 @@
         "sysui",
         "tcpip",
         "tinyh",
+        "tsbuildinfo",
         "uifabric",
         "webadb",
         "websockify",

packages/adb-backend-web/package.json

@@ -9,7 +9,9 @@
     "author": "Simon Chan <cnsimonchan@live.com>",
     "homepage": "https://github.com/yume-chan/ya-webadb#readme",
     "license": "MIT",
-    "main": "lib/index.js",
+    "main": "cjs/index.js",
+    "module": "esm/index.js",
+    "types": "dts/index.d.ts",
     "repository": {
         "type": "git",
         "url": "git+https://github.com/yume-chan/ya-webadb.git"

packages/adb-backend-web/tsconfig.json

@@ -1,13 +1,24 @@
 {
     "extends": "../../tsconfig.base.json",
     "compilerOptions": {
-        "outDir": "lib", //                       /* Redirect output structure to the directory. */
+        "outDir": "esm",
-        "rootDir": "./src", //                    /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        "declarationDir": "dts",
+        "rootDir": "./src",
         "lib": [
             "ESNext",
             "DOM"
+        ],
+        "types": [
+            "@types/w3c-web-usb",
+            "@yume-chan/adb"
         ]
     },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "src/**/*.spec.ts"
+    ],
     "references": [
         {
             "path": "../adb/tsconfig.json"

packages/adb/package.json

@@ -8,7 +8,9 @@
     "author": "Simon Chan <cnsimonchan@live.com>",
     "homepage": "https://github.com/yume-chan/ya-webadb#readme",
     "license": "MIT",
-    "main": "lib/index.js",
+    "main": "cjs/index.js",
+    "module": "esm/index.js",
+    "types": "dts/index.d.ts",
     "repository": {
         "type": "git",
         "url": "git+https://github.com/yume-chan/ya-webadb.git"

packages/adb/src/packet.ts

@@ -1,4 +1,4 @@
-import { BackingField, Struct, StructInitType, StructValueType } from '@yume-chan/struct';
+import { Struct, StructInitType, StructValueType } from '@yume-chan/struct';
 import { AdbBackend } from './backend';
 import { BufferedStream } from './stream';
 
@@ -11,7 +11,7 @@ export enum AdbCommand {
     Write = 0x45545257,   // 'WRTE'
 }
 
-const AdbPacketWithoutPayload =
+const AdbPacketHeader =
     new Struct({ littleEndian: true })
         .uint32('command', undefined)
         .uint32('arg0')
@@ -21,13 +21,8 @@ const AdbPacketWithoutPayload =
         .int32('magic');
 
 const AdbPacketStruct =
-    AdbPacketWithoutPayload
+    AdbPacketHeader
-        .arrayBuffer('payload', { lengthField: 'payloadLength' })
+        .arrayBuffer('payload', { lengthField: 'payloadLength' });
-        .afterParsed((value) => {
-            if (value[BackingField].magic !== value.magic) {
-                throw new Error('Invalid command');
-            }
-        });
 
 export type AdbPacket = StructValueType<typeof AdbPacketStruct>;
 
@@ -37,7 +32,7 @@ export namespace AdbPacket {
     export function create(
         init: AdbPacketInit,
         calculateChecksum: boolean,
-        backend: AdbBackend
+        backend: AdbBackend,
     ): AdbPacket {
         let checksum: number;
         if (calculateChecksum && init.payload) {
@@ -85,8 +80,9 @@ export namespace AdbPacket {
 
     export async function write(packet: AdbPacket, backend: AdbBackend): Promise<void> {
         // Write payload separately to avoid an extra copy
-        await backend.write(AdbPacketWithoutPayload.serialize(packet, backend));
+        const header = AdbPacketHeader.serialize(packet, backend);
-        if (packet.payload) {
+        await backend.write(header);
+        if (packet.payload.byteLength) {
             await backend.write(packet.payload);
         }
     }

packages/adb/src/socket/dispatcher.ts

@@ -23,6 +23,8 @@ export interface AdbIncomingSocketEventArgs {
     socket: AdbSocket;
 }
 
+const EmptyArrayBuffer = new ArrayBuffer(0);
+
 export class AdbPacketDispatcher extends AutoDisposable {
     // ADB socket id starts from 1
     // (0 means open failed)
@@ -222,10 +224,10 @@ export class AdbPacketDispatcher extends AutoDisposable {
         packetOrCommand: AdbPacketInit | AdbCommand,
         arg0?: number,
         arg1?: number,
-        payload?: string | ArrayBuffer
+        payload: string | ArrayBuffer = EmptyArrayBuffer,
     ): Promise<void> {
         let init: AdbPacketInit;
-        if (arguments.length === 1) {
+        if (arg0 === undefined) {
             init = packetOrCommand as AdbPacketInit;
         } else {
             init = {

packages/adb/tsconfig.json

@@ -1,15 +1,23 @@
 {
     "extends": "../../tsconfig.base.json",
     "compilerOptions": {
-        "outDir": "lib", //                       /* Redirect output structure to the directory. */
+        "target": "ES2016",
-        "rootDir": "./src", //                    /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        "outDir": "esm",
+        "declarationDir": "dts",
+        "rootDir": "./src"
     },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "src/**/*.spec.ts"
+    ],
     "references": [
         {
-            "path": "../event/tsconfig.json"
+            "path": "../event/tsconfig.esm.json"
         },
         {
-            "path": "../struct/tsconfig.json"
+            "path": "../struct/tsconfig.esm.json"
         }
     ]
 }

packages/demo/src/routes/device-info.tsx

@@ -1,4 +1,4 @@
-import { Icon, MessageBar, StackItem, TooltipHost, Text, Separator } from '@fluentui/react';
+import { Icon, MessageBar, Separator, TooltipHost } from '@fluentui/react';
 import { AdbFeatures } from '@yume-chan/adb';
 import React from 'react';
 import { ExternalLink } from '../components';

packages/demo/tsconfig.json

@@ -2,15 +2,32 @@
     "extends": "../../tsconfig.base.json",
     "compilerOptions": {
         "rootDir": "./src", //                    /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        "target": "ES2016",
         "lib": [
             "ESNext",
             "DOM"
         ],
         "jsx": "react", //                        /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
-        "declaration": false, //                  /* Generates corresponding '.d.ts' file. */
-        "declarationMap": false, //               /* Generates a sourcemap for each corresponding '.d.ts' file. */
         "composite": false, //                    /* Enable project compilation */
+        "types": [
+            "@types/node",
+            "@types/react",
+            "@types/react-dom",
+            "@types/react-router-dom",
+            "@fluentui/react",
+            "@yume-chan/adb",
+            "@yume-chan/adb-backend-web",
+            "@yume-chan/async-operation-manager",
+            "@yume-chan/event",
+            "@yume-chan/struct"
+        ]
     },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "src/**/*.spec.ts"
+    ],
     "references": [
         {
             "path": "../adb-backend-web/tsconfig.json"

packages/event/package.json

@@ -5,25 +5,39 @@
     "keywords": [
         "event"
     ],
-    "author": "Simon Chan <cnsimonchan@live.com>",
-    "homepage": "https://github.com/yume-chan/ya-webadb#readme",
     "license": "MIT",
-    "main": "lib/index.js",
+    "author": {
+        "name": "Simon Chan",
+        "email": "cnsimonchan@live.com",
+        "url": "https://chensi.moe/blog"
+    },
+    "homepage": "https://github.com/yume-chan/ya-webadb/tree/master/packages/event#readme",
     "repository": {
         "type": "git",
-        "url": "git+https://github.com/yume-chan/ya-webadb.git"
+        "url": "git+https://github.com/yume-chan/ya-webadb.git",
-    },
+        "directory": "packages/event"
-    "scripts": {
-        "build": "tsc -b",
-        "build:watch": "tsc -b -w"
     },
     "bugs": {
         "url": "https://github.com/yume-chan/ya-webadb/issues"
     },
-    "devDependencies": {
+    "main": "cjs/index.js",
-        "typescript": "4.1.3"
+    "module": "esm/index.js",
+    "types": "dts/index.d.ts",
+    "scripts": {
+        "build": "rimraf {cjs,esm,dts,*.tsbuildinfo} && tsc -b tsconfig.esm.json tsconfig.cjs.json",
+        "build:watch": "tsc -b -w tsconfig.esm.json tsconfig.cjs.json",
+        "test": "jest",
+        "coverage": "jest --coverage",
+        "prepublishOnly": "npm run build"
     },
     "dependencies": {
         "tslib": "2.0.3"
+    },
+    "devDependencies": {
+        "@types/jest": "26.0.19",
+        "jest": "26.6.3",
+        "rimraf": "3.0.2",
+        "ts-jest": "26.4.4",
+        "typescript": "4.1.3"
     }
 }

packages/event/tsconfig.cjs.json

@@ -0,0 +1,11 @@
+{
+    "extends": "./tsconfig.esm.json",
+    "compilerOptions": {
+        "composite": false,
+        "module": "CommonJS",
+        "outDir": "cjs",
+        "declaration": false,
+        "declarationDir": null,
+        "declarationMap": false
+    }
+}

packages/event/tsconfig.esm.json

@@ -0,0 +1,15 @@
+{
+    "extends": "../../tsconfig.base.json",
+    "compilerOptions": {
+        "rootDir": "src",
+        "outDir": "esm",
+        "declarationDir": "dts",
+        "types": [],
+    },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "src/**/*.spec.ts"
+    ]
+}

packages/event/tsconfig.json

@@ -1,7 +1,10 @@
 {
-    "extends": "../../tsconfig.base.json",
+    "extends": "./tsconfig.esm.json",
     "compilerOptions": {
-        "outDir": "lib", //                       /* Redirect output structure to the directory. */
+        "noEmit": true,
-        "rootDir": "./src" //                     /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        "types": [
-    }
+            "jest"
+        ]
+    },
+    "exclude": []
 }

packages/struct/.npmignore

@@ -0,0 +1,10 @@
+.github
+.vscode
+coverage
+src/**.spec.ts
+
+jest.config.js
+pnpm-lock.yaml
+renovate.json
+tsconfig.json
+*.tsbuildinfo

packages/struct/jest.config.js

@@ -0,0 +1,4 @@
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+};

packages/struct/package.json

@@ -6,25 +6,39 @@
         "structure",
         "typescript"
     ],
-    "author": "Simon Chan <cnsimonchan@live.com>",
-    "homepage": "https://github.com/yume-chan/ya-webadb#readme",
     "license": "MIT",
-    "main": "lib/index.js",
+    "author": {
+        "name": "Simon Chan",
+        "email": "cnsimonchan@live.com",
+        "url": "https://chensi.moe/blog"
+    },
+    "homepage": "https://github.com/yume-chan/ya-webadb/tree/master/packages/struct#readme",
     "repository": {
         "type": "git",
-        "url": "git+https://github.com/yume-chan/ya-webadb.git"
+        "url": "git+https://github.com/yume-chan/ya-webadb.git",
-    },
+        "directory": "packages/struct"
-    "scripts": {
-        "build": "tsc -b",
-        "build:watch": "tsc -b -w"
     },
     "bugs": {
         "url": "https://github.com/yume-chan/ya-webadb/issues"
     },
-    "devDependencies": {
+    "main": "cjs/index.js",
-        "typescript": "4.1.3"
+    "module": "esm/index.js",
+    "types": "dts/index.d.ts",
+    "scripts": {
+        "build": "rimraf {cjs,esm,dts,*.tsbuildinfo} && tsc -b tsconfig.esm.json tsconfig.cjs.json",
+        "build:watch": "tsc -b -w tsconfig.esm.json tsconfig.cjs.json",
+        "test": "jest",
+        "coverage": "jest --coverage",
+        "prepublishOnly": "npm run build"
     },
     "dependencies": {
         "tslib": "2.0.3"
+    },
+    "devDependencies": {
+        "@types/jest": "26.0.19",
+        "jest": "26.6.3",
+        "rimraf": "3.0.2",
+        "ts-jest": "26.4.4",
+        "typescript": "4.1.3"
     }
 }

packages/struct/src/backing-field.ts

@@ -1,20 +0,0 @@
-export const BackingField = Symbol('BackingField');
-
-export function getBackingField<T = unknown>(object: unknown, field: string): T {
-    return (object as any)[BackingField][field] as T;
-}
-
-export function setBackingField(object: unknown, field: string, value: any): void {
-    (object as any)[BackingField][field] = value;
-}
-
-export function defineSimpleAccessors(object: unknown, field: string): void {
-    Object.defineProperty(object, field, {
-        configurable: true,
-        enumerable: true,
-        get() { return getBackingField(object, field); },
-        set(value) { setBackingField(object, field, value); },
-    });
-}
-
-export type WithBackingField<T> = T & { [BackingField]: any; };

packages/struct/src/field/array.ts

@@ -1,67 +0,0 @@
-import { getBackingField, setBackingField } from '../backing-field';
-import { FieldDescriptorBase, FieldDescriptorBaseOptions } from './descriptor';
-
-export namespace Array {
-    export enum SubType {
-        ArrayBuffer,
-        String,
-    }
-
-    export type TypeScriptType<TType extends SubType = SubType> =
-        TType extends SubType.ArrayBuffer ? ArrayBuffer :
-        TType extends SubType.String ? string :
-        ArrayBuffer | string;
-
-    export interface BackingField {
-        buffer?: ArrayBuffer;
-
-        string?: string;
-    }
-
-    export function initialize(object: any, field: Array, value: BackingField): void {
-        switch (field.subType) {
-            case SubType.ArrayBuffer:
-                Object.defineProperty(object, field.name, {
-                    configurable: true,
-                    enumerable: true,
-                    get(): ArrayBuffer {
-                        return getBackingField<BackingField>(object, field.name).buffer!;
-                    },
-                    set(buffer: ArrayBuffer) {
-                        setBackingField(object, field.name, { buffer });
-                    },
-                });
-                break;
-            case SubType.String:
-                Object.defineProperty(object, field.name, {
-                    configurable: true,
-                    enumerable: true,
-                    get(): string {
-                        return getBackingField<BackingField>(object, field.name).string!;
-                    },
-                    set(string: string) {
-                        setBackingField(object, field.name, { string });
-                    },
-                });
-                break;
-            default:
-                throw new Error('Unknown type');
-        }
-        setBackingField(object, field.name, value);
-    }
-}
-
-export interface Array<
-    TName extends string = string,
-    TType extends Array.SubType = Array.SubType,
-    TResultObject = {},
-    TInitObject = {},
-    TOptions extends FieldDescriptorBaseOptions = FieldDescriptorBaseOptions
-    > extends FieldDescriptorBase<
-    TName,
-    TResultObject,
-    TInitObject,
-    TOptions
-    > {
-    subType: TType;
-}

packages/struct/src/field/definition.ts

@@ -1,64 +0,0 @@
-import { StructDeserializationContext, StructOptions, StructSerializationContext } from '../types';
-import { FieldDescriptorBase, FieldType } from './descriptor';
-
-export interface FieldTypeDefinition<
-    TDescriptor extends FieldDescriptorBase = FieldDescriptorBase,
-    TInitExtra = undefined,
-    > {
-    type: FieldType | string;
-
-    deserialize(options: {
-        context: StructDeserializationContext;
-        field: TDescriptor;
-        object: any;
-        options: StructOptions;
-    }): Promise<{ value: any; extra?: TInitExtra; }>;
-
-    getSize(options: {
-        field: TDescriptor;
-        options: StructOptions;
-    }): number;
-
-    getDynamicSize?(options: {
-        context: StructSerializationContext;
-        field: TDescriptor;
-        object: any;
-        options: StructOptions;
-    }): number;
-
-    initialize?(options: {
-        context: StructSerializationContext;
-        field: TDescriptor;
-        value: any;
-        extra?: TInitExtra;
-        object: any;
-        options: StructOptions;
-    }): void;
-
-    serialize(options: {
-        context: StructSerializationContext;
-        dataView: DataView;
-        field: TDescriptor;
-        object: any;
-        offset: number;
-        options: StructOptions;
-    }): void;
-}
-
-const registry: Record<number | string, FieldTypeDefinition<any, any>> = {};
-
-export function getFieldTypeDefinition(type: FieldType | string): FieldTypeDefinition<any, any> {
-    return registry[type];
-}
-
-export function registerFieldTypeDefinition<
-    TDescriptor extends FieldDescriptorBase,
-    TInitExtra,
-    TDefinition extends FieldTypeDefinition<TDescriptor, TInitExtra>
->(
-    _field: TDescriptor,
-    _initExtra: TInitExtra,
-    methods: TDefinition
-): void {
-    registry[methods.type] = methods;
-}

packages/struct/src/field/fixed-length-array.ts

@@ -1,82 +0,0 @@
-import { getBackingField } from '../backing-field';
-import { placeholder } from '../utils';
-import { Array } from './array';
-import { registerFieldTypeDefinition } from './definition';
-import { FieldDescriptorBaseOptions, FieldType } from './descriptor';
-
-export namespace FixedLengthArray {
-    export interface Options extends FieldDescriptorBaseOptions {
-        length: number;
-    }
-}
-
-export interface FixedLengthArray<
-    TName extends string = string,
-    TType extends Array.SubType = Array.SubType,
-    TTypeScriptType = Array.TypeScriptType<TType>,
-    TOptions extends FixedLengthArray.Options = FixedLengthArray.Options
-    > extends Array<
-    TName,
-    TType,
-    Record<TName, TTypeScriptType>,
-    Record<TName, TTypeScriptType>,
-    TOptions
-    > {
-    type: FieldType.FixedLengthArray;
-
-    options: TOptions;
-};
-
-registerFieldTypeDefinition(
-    placeholder<FixedLengthArray>(),
-    placeholder<ArrayBuffer>(),
-    {
-        type: FieldType.FixedLengthArray,
-
-        async deserialize(
-            { context, field }
-        ): Promise<{ value: string | ArrayBuffer, extra?: ArrayBuffer; }> {
-            const buffer = await context.read(field.options.length);
-
-            switch (field.subType) {
-                case Array.SubType.ArrayBuffer:
-                    return { value: buffer };
-                case Array.SubType.String:
-                    return {
-                        value: context.decodeUtf8(buffer),
-                        extra: buffer
-                    };
-                default:
-                    throw new Error('Unknown type');
-            }
-        },
-
-        getSize({ field }) {
-            return field.options.length;
-        },
-
-        initialize({ extra, field, object, value }) {
-            const backingField: Array.BackingField = {};
-            if (typeof value === 'string') {
-                backingField.string = value;
-                if (extra) {
-                    backingField.buffer = extra;
-                }
-            } else {
-                backingField.buffer = value;
-            }
-            Array.initialize(object, field, backingField);
-        },
-
-        serialize({ context, dataView, field, object, offset }) {
-            const backingField = getBackingField<Array.BackingField>(object, field.name);
-            backingField.buffer ??=
-                context.encodeUtf8(backingField.string!);
-
-            new Uint8Array(dataView.buffer).set(
-                new Uint8Array(backingField.buffer),
-                offset
-            );
-        }
-    }
-);

packages/struct/src/field/index.ts

@@ -1,6 +0,0 @@
-export * from './array';
-export * from './definition';
-export * from './descriptor';
-export * from './fixed-length-array';
-export * from './number';
-export * from './variable-length-array';

packages/struct/src/field/number.ts

@@ -1,92 +0,0 @@
-import { placeholder } from '../utils';
-import { registerFieldTypeDefinition } from './definition';
-import { FieldDescriptorBase, FieldDescriptorBaseOptions, FieldType } from './descriptor';
-
-export namespace Number {
-    export type TypeScriptType<T extends SubType> =
-        T extends SubType.Uint64 ? bigint :
-        T extends SubType.Int64 ? bigint :
-        number;
-
-    export enum SubType {
-        Uint8,
-        Uint16,
-        Int32,
-        Uint32,
-        Uint64,
-        Int64,
-    }
-
-    export const SizeMap: Record<SubType, number> = {
-        [SubType.Uint8]: 1,
-        [SubType.Uint16]: 2,
-        [SubType.Int32]: 4,
-        [SubType.Uint32]: 4,
-        [SubType.Uint64]: 8,
-        [SubType.Int64]: 8,
-    };
-
-    export const DataViewGetterMap = {
-        [SubType.Uint8]: 'getUint8',
-        [SubType.Uint16]: 'getUint16',
-        [SubType.Int32]: 'getInt32',
-        [SubType.Uint32]: 'getUint32',
-        [SubType.Uint64]: 'getBigUint64',
-        [SubType.Int64]: 'getBigInt64',
-    } as const;
-
-    export const DataViewSetterMap = {
-        [SubType.Uint8]: 'setUint8',
-        [SubType.Uint16]: 'setUint16',
-        [SubType.Int32]: 'setInt32',
-        [SubType.Uint32]: 'setUint32',
-        [SubType.Uint64]: 'setBigUint64',
-        [SubType.Int64]: 'setBigInt64',
-    } as const;
-}
-
-export interface Number<
-    TName extends string = string,
-    TSubType extends Number.SubType = Number.SubType,
-    TTypeScriptType = Number.TypeScriptType<TSubType>,
-    TOptions extends FieldDescriptorBaseOptions = FieldDescriptorBaseOptions
-    > extends FieldDescriptorBase<
-    TName,
-    Record<TName, TTypeScriptType>,
-    Record<TName, TTypeScriptType>,
-    TOptions
-    > {
-    type: FieldType.Number;
-
-    subType: TSubType;
-}
-
-registerFieldTypeDefinition(
-    placeholder<Number>(),
-    undefined,
-    {
-        type: FieldType.Number,
-
-        getSize({ field }) {
-            return Number.SizeMap[field.subType];
-        },
-
-        async deserialize({ context, field, options }) {
-            const buffer = await context.read(Number.SizeMap[field.subType]);
-            const view = new DataView(buffer);
-            const value = view[Number.DataViewGetterMap[field.subType]](
-                0,
-                options.littleEndian
-            );
-            return { value };
-        },
-
-        serialize({ dataView, field, object, offset, options }) {
-            (dataView[Number.DataViewSetterMap[field.subType]] as any)(
-                offset,
-                object[field.name],
-                options.littleEndian
-            );
-        },
-    }
-);

packages/struct/src/field/variable-length-array.ts

@@ -1,221 +0,0 @@
-import { getBackingField, setBackingField } from '../backing-field';
-import { StructSerializationContext } from '../types';
-import { Identity, placeholder } from '../utils';
-import { Array } from './array';
-import { registerFieldTypeDefinition } from './definition';
-import { FieldDescriptorBaseOptions, FieldType } from './descriptor';
-
-export namespace VariableLengthArray {
-    export type TypeScriptTypeCanBeUndefined<
-        TEmptyBehavior extends EmptyBehavior = EmptyBehavior
-        > =
-        TEmptyBehavior extends EmptyBehavior.Empty ? never :
-        undefined;
-
-    export type TypeScriptType<
-        TType extends Array.SubType = Array.SubType,
-        TEmptyBehavior extends EmptyBehavior = EmptyBehavior
-        > =
-        Identity<
-            Array.TypeScriptType<TType> |
-            TypeScriptTypeCanBeUndefined<TEmptyBehavior>
-        >;
-
-    export enum EmptyBehavior {
-        Undefined,
-        Empty,
-    }
-
-    export type KeyOfType<TObject, TProperty> =
-        {
-            [TKey in keyof TObject]:
-            TObject[TKey] extends TProperty ? TKey : never
-        }[keyof TObject];
-
-    export interface Options<
-        TInit = object,
-        TLengthField extends KeyOfType<TInit, number | string> = any,
-        TEmptyBehavior extends EmptyBehavior = EmptyBehavior
-        > extends FieldDescriptorBaseOptions {
-        lengthField: TLengthField;
-
-        emptyBehavior?: TEmptyBehavior;
-    }
-
-    export function getLengthBackingField(
-        object: any,
-        field: VariableLengthArray
-    ): number | undefined {
-        return getBackingField<number>(object, field.options.lengthField);
-    }
-
-    export function setLengthBackingField(
-        object: any,
-        field: VariableLengthArray,
-        value: number | undefined
-    ) {
-        setBackingField(object, field.options.lengthField, value);
-    }
-
-    export function initialize(
-        object: any,
-        field: VariableLengthArray,
-        value: Array.BackingField,
-        context: StructSerializationContext,
-    ): void {
-        Array.initialize(object, field, value);
-        const descriptor = Object.getOwnPropertyDescriptor(object, field.name)!;
-        delete object[field.name];
-
-        switch (field.subType) {
-            case Array.SubType.ArrayBuffer:
-                Object.defineProperty(object, field.name, {
-                    ...descriptor,
-                    set(buffer: ArrayBuffer | undefined) {
-                        descriptor.set!.call(object, buffer);
-                        setLengthBackingField(object, field, buffer?.byteLength ?? 0);
-                    },
-                });
-
-                delete object[field.options.lengthField];
-                Object.defineProperty(object, field.options.lengthField, {
-                    configurable: true,
-                    enumerable: true,
-                    get() {
-                        return getLengthBackingField(object, field);
-                    }
-                });
-                break;
-            case Array.SubType.String:
-                Object.defineProperty(object, field.name, {
-                    ...descriptor,
-                    set(string: string | undefined) {
-                        descriptor.set!.call(object, string);
-                        if (string) {
-                            setLengthBackingField(object, field, undefined);
-                        } else {
-                            setLengthBackingField(object, field, 0);
-                        }
-                    },
-                });
-
-                delete object[field.options.lengthField];
-                Object.defineProperty(object, field.options.lengthField, {
-                    configurable: true,
-                    enumerable: true,
-                    get() {
-                        let value = getLengthBackingField(object, field);
-                        if (value === undefined) {
-                            const backingField = getBackingField<Array.BackingField>(object, field.name);
-                            const buffer = context.encodeUtf8(backingField.string!);
-                            backingField.buffer = buffer;
-
-                            value = buffer.byteLength;
-                            setLengthBackingField(object, field, value);
-                        }
-                        return value;
-                    }
-                });
-                break;
-            default:
-                throw new Error('Unknown type');
-        }
-        setBackingField(object, field.name, value);
-        if (value.buffer) {
-            setLengthBackingField(object, field, value.buffer.byteLength);
-        }
-    }
-}
-
-export interface VariableLengthArray<
-    TName extends string = string,
-    TType extends Array.SubType = Array.SubType,
-    TInit = object,
-    TLengthField extends VariableLengthArray.KeyOfType<TInit, number | string> = any,
-    TEmptyBehavior extends VariableLengthArray.EmptyBehavior = VariableLengthArray.EmptyBehavior,
-    TTypeScriptType = VariableLengthArray.TypeScriptType<TType, TEmptyBehavior>,
-    TOptions extends VariableLengthArray.Options<TInit, TLengthField, TEmptyBehavior> = VariableLengthArray.Options<TInit, TLengthField, TEmptyBehavior>
-    > extends Array<
-    TName,
-    TType,
-    Record<TName, TTypeScriptType>,
-    Record<TName, TTypeScriptType> & Record<TLengthField, never>,
-    TOptions
-    > {
-    type: FieldType.VariableLengthArray;
-
-    options: TOptions;
-}
-
-registerFieldTypeDefinition(
-    placeholder<VariableLengthArray>(),
-    placeholder<ArrayBuffer>(),
-    {
-        type: FieldType.VariableLengthArray,
-
-        async deserialize(
-            { context, field, object }
-        ): Promise<{ value: string | ArrayBuffer | undefined, extra?: ArrayBuffer; }> {
-            let length = object[field.options.lengthField];
-            if (typeof length === 'string') {
-                length = Number.parseInt(length, 10);
-            }
-
-            if (length === 0) {
-                if (field.options.emptyBehavior === VariableLengthArray.EmptyBehavior.Empty) {
-                    switch (field.subType) {
-                        case Array.SubType.ArrayBuffer:
-                            return { value: new ArrayBuffer(0) };
-                        case Array.SubType.String:
-                            return { value: '', extra: new ArrayBuffer(0) };
-                        default:
-                            throw new Error('Unknown type');
-                    }
-                } else {
-                    return { value: undefined };
-                }
-            }
-
-            const buffer = await context.read(length);
-            switch (field.subType) {
-                case Array.SubType.ArrayBuffer:
-                    return { value: buffer };
-                case Array.SubType.String:
-                    return {
-                        value: context.decodeUtf8(buffer),
-                        extra: buffer
-                    };
-                default:
-                    throw new Error('Unknown type');
-            }
-        },
-
-        getSize() { return 0; },
-
-        getDynamicSize({ field, object }) {
-            return object[field.options.lengthField];
-        },
-
-        initialize({ context, extra, field, object, value }) {
-            const backingField: Array.BackingField = {};
-            if (typeof value === 'string') {
-                backingField.string = value;
-                if (extra) {
-                    backingField.buffer = extra;
-                }
-            } else {
-                backingField.buffer = value;
-            }
-            Array.initialize(object, field, backingField);
-            VariableLengthArray.initialize(object, field, backingField, context);
-        },
-
-        serialize({ dataView, field, object, offset }) {
-            const backingField = getBackingField<Array.BackingField>(object, field.name);
-            new Uint8Array(dataView.buffer).set(
-                new Uint8Array(backingField.buffer!),
-                offset
-            );
-        },
-    }
-);

packages/struct/src/index.ts

@@ -1,6 +1,4 @@
-export * from './backing-field';
+export * from './runtime';
-export * from './field';
 export * from './struct';
 export { default as Struct } from './struct';
 export * from './types';
-export * from './utils';

packages/struct/src/runtime/context.spec.ts

@@ -0,0 +1,14 @@
+import { StructDefaultOptions } from './context';
+import { GlobalStructFieldRuntimeTypeRegistry } from './registry';
+
+describe('Runtime', () => {
+    describe('StructDefaultOptions', () => {
+        it('should have `littleEndian` equals to `false`', () => {
+            expect(StructDefaultOptions.littleEndian).toBe(false);
+        });
+
+        it('should have `fieldRuntimeTypeRegistry` equals to `GlobalStructFieldRuntimeTypeRegistry`', () => {
+            expect(StructDefaultOptions.fieldRuntimeTypeRegistry).toBe(GlobalStructFieldRuntimeTypeRegistry);
+        });
+    });
+});

packages/struct/src/runtime/context.ts

@@ -0,0 +1,45 @@
+import type { StructFieldRuntimeTypeRegistry } from './registry';
+import { GlobalStructFieldRuntimeTypeRegistry } from './registry';
+
+/**
+ * Context with enough methods to serialize a struct
+ */
+export interface StructSerializationContext {
+    /**
+     * Encode the specified string into an ArrayBuffer using UTF-8 encoding
+     */
+    encodeUtf8(input: string): ArrayBuffer;
+}
+
+/**
+ * Context with enough methods to deserialize a struct
+ */
+export interface StructDeserializationContext extends StructSerializationContext {
+    /**
+     * Decode the specified `ArrayBuffer` using UTF-8 encoding
+     */
+    decodeUtf8(buffer: ArrayBuffer): string;
+
+    /**
+     * Read exactly `length` bytes of data from underlying storage.
+     *
+     * Errors can be thrown to indicates end of file or other errors.
+     */
+    read(length: number): ArrayBuffer | Promise<ArrayBuffer>;
+}
+
+export interface StructOptions {
+    /**
+     * Whether multi-byte fields in this struct are in little endian
+     *
+     * Default to `false`
+     */
+    littleEndian: boolean;
+
+    fieldRuntimeTypeRegistry: StructFieldRuntimeTypeRegistry;
+}
+
+export const StructDefaultOptions: Readonly<StructOptions> = {
+    littleEndian: false,
+    fieldRuntimeTypeRegistry: GlobalStructFieldRuntimeTypeRegistry,
+};

packages/struct/src/runtime/descriptor.ts

@@ -1,7 +1,7 @@
-export enum FieldType {
+export enum BuiltInFieldType {
     Number,
-    FixedLengthArray,
+    FixedLengthArrayBufferLike,
-    VariableLengthArray,
+    VariableLengthArrayBufferLike,
 }
 
 export interface FieldDescriptorBaseOptions {
@@ -14,7 +14,7 @@ export interface FieldDescriptorBase<
     TInitObject = {},
     TOptions extends FieldDescriptorBaseOptions = FieldDescriptorBaseOptions
     > {
-    type: FieldType | string;
+    type: BuiltInFieldType | string;
 
     name: TName;
 

packages/struct/src/runtime/index.ts

@@ -0,0 +1,5 @@
+export * from './context';
+export * from './descriptor';
+export * from './registry';
+export * from './runtime-type';
+export * from './runtime-value';

packages/struct/src/runtime/registry.spec.ts

@@ -0,0 +1,61 @@
+import { StructDeserializationContext, StructSerializationContext } from './context';
+import { GlobalStructFieldRuntimeTypeRegistry, StructFieldRuntimeTypeRegistry } from './registry';
+import { FieldRuntimeValue } from './runtime-type';
+
+describe('Runtime', () => {
+    describe('StructFieldRuntimeTypeRegistry', () => {
+        it('should be able to get registered type', () => {
+            const registry = new StructFieldRuntimeTypeRegistry();
+
+            const type = 'mock';
+            const MockFieldRuntimeValue = class extends FieldRuntimeValue {
+                static getSize() { return 0; }
+                public deserialize(context: StructDeserializationContext): void | Promise<void> {
+                    throw new Error('Method not implemented.');
+                }
+                public get(): unknown {
+                    throw new Error('Method not implemented.');
+                }
+                public set(value: unknown): void {
+                    throw new Error('Method not implemented.');
+                }
+                public serialize(dataView: DataView, offset: number, context: StructSerializationContext): void {
+                    throw new Error('Method not implemented.');
+                }
+            };
+
+            registry.register(type, MockFieldRuntimeValue);
+            expect(registry.get(type)).toBe(MockFieldRuntimeValue);
+        });
+
+        it('should throw an error if same type been registered twice', () => {
+            const registry = new StructFieldRuntimeTypeRegistry();
+
+            const type = 'mock';
+            const MockFieldRuntimeValue = class extends FieldRuntimeValue {
+                static getSize() { return 0; }
+                public deserialize(context: StructDeserializationContext): void | Promise<void> {
+                    throw new Error('Method not implemented.');
+                }
+                public get(): unknown {
+                    throw new Error('Method not implemented.');
+                }
+                public set(value: unknown): void {
+                    throw new Error('Method not implemented.');
+                }
+                public serialize(dataView: DataView, offset: number, context: StructSerializationContext): void {
+                    throw new Error('Method not implemented.');
+                }
+            };
+
+            registry.register(type, MockFieldRuntimeValue);
+            expect(() => registry.register(type, MockFieldRuntimeValue)).toThrowError();
+        });
+    });
+
+    describe('GlobalStructFieldRuntimeTypeRegistry', () => {
+        it('should be defined', () => {
+            expect(GlobalStructFieldRuntimeTypeRegistry).toBeInstanceOf(StructFieldRuntimeTypeRegistry);
+        });
+    });
+});

packages/struct/src/runtime/registry.ts

@@ -0,0 +1,26 @@
+import type { BuiltInFieldType } from './descriptor';
+import type { FieldRuntimeType } from './runtime-type';
+
+export class StructFieldRuntimeTypeRegistry {
+    private store: Record<number | string, FieldRuntimeType> = {};
+
+    public get(
+        type: BuiltInFieldType | string
+    ): FieldRuntimeType {
+        return this.store[type];
+    }
+
+    public register<
+        TConstructor extends FieldRuntimeType<any>
+    >(
+        type: BuiltInFieldType | string,
+        Constructor: TConstructor
+    ): void {
+        if (type in this.store) {
+            throw new Error(`Struct field runtime type '${type}' has already been registered`);
+        }
+        this.store[type] = Constructor;
+    }
+}
+
+export const GlobalStructFieldRuntimeTypeRegistry = new StructFieldRuntimeTypeRegistry();

packages/struct/src/runtime/runtime-type.spec.ts

@@ -0,0 +1,27 @@
+import { StructDeserializationContext, StructSerializationContext } from './context';
+import { FieldRuntimeValue } from './runtime-type';
+
+describe('Runtime', () => {
+    describe('FieldRuntimeValue', () => {
+        it('`getSize` should return same value as static `getSize`', () => {
+            class MockFieldRuntimeValue extends FieldRuntimeValue {
+                static getSize() { return 42; }
+                public deserialize(context: StructDeserializationContext): void | Promise<void> {
+                    throw new Error('Method not implemented.');
+                }
+                public get(): unknown {
+                    throw new Error('Method not implemented.');
+                }
+                public set(value: unknown): void {
+                    throw new Error('Method not implemented.');
+                }
+                public serialize(dataView: DataView, offset: number, context: StructSerializationContext): void {
+                    throw new Error('Method not implemented.');
+                }
+            }
+
+            const instance = new MockFieldRuntimeValue(undefined as any, undefined as any, undefined as any, undefined as any);
+            expect(instance.getSize()).toBe(42);
+        });
+    });
+});

packages/struct/src/runtime/runtime-type.ts

@@ -0,0 +1,45 @@
+import type { StructDeserializationContext, StructOptions, StructSerializationContext } from './context';
+import type { FieldDescriptorBase } from './descriptor';
+
+export abstract class FieldRuntimeValue<TDescriptor extends FieldDescriptorBase = FieldDescriptorBase> {
+    public readonly descriptor: TDescriptor;
+
+    public readonly options: Readonly<StructOptions>;
+
+    public readonly context: StructSerializationContext;
+
+    public constructor(
+        descriptor: TDescriptor,
+        options: Readonly<StructOptions>,
+        context: StructSerializationContext,
+        object: any,
+    ) {
+        this.descriptor = descriptor;
+        this.options = options;
+        this.context = context;
+    }
+
+    public abstract deserialize(context: StructDeserializationContext, object: any): void | Promise<void>;
+
+    public getSize(): number {
+        const Constructor = Object.getPrototypeOf(this).constructor as FieldRuntimeType<TDescriptor>;
+        return Constructor.getSize(this.descriptor, this.options);
+    }
+
+    public abstract get(): unknown;
+
+    public abstract set(value: unknown): void;
+
+    public abstract serialize(dataView: DataView, offset: number, context: StructSerializationContext): void;
+}
+
+export interface FieldRuntimeType<TDescriptor extends FieldDescriptorBase = FieldDescriptorBase> {
+    new(
+        descriptor: TDescriptor,
+        options: Readonly<StructOptions>,
+        context: StructSerializationContext,
+        object: any,
+    ): FieldRuntimeValue<TDescriptor>;
+
+    getSize(descriptor: TDescriptor, options: Readonly<StructOptions>): number;
+}

packages/struct/src/runtime/runtime-value.spec.ts

@@ -0,0 +1,34 @@
+import { createObjectWithRuntimeValues, getRuntimeValue, setRuntimeValue } from './runtime-value';
+
+describe('Runtime', () => {
+    describe('RuntimeValue', () => {
+        it('`createObjectWithRuntimeValues` should create an object with symbol', () => {
+            const object = createObjectWithRuntimeValues();
+            expect(Object.getOwnPropertySymbols(object)).toHaveLength(1);
+        });
+
+        it('`getRuntimeValue` should return previously set value', () => {
+            const object = createObjectWithRuntimeValues();
+            const field = 'foo';
+            const value = {} as any;
+            setRuntimeValue(object, field, value);
+            expect(getRuntimeValue(object, field)).toBe(value);
+        });
+
+        it('`setRuntimeValue` should define a proxy to underlying `RuntimeValue`', () => {
+            const object = createObjectWithRuntimeValues();
+            const field = 'foo';
+            const getter = jest.fn(() => 42);
+            const setter = jest.fn((value: number) => { });
+            const value = { get: getter, set: setter } as any;
+            setRuntimeValue(object, field, value);
+
+            expect((object as any)[field]).toBe(42);
+            expect(getter).toBeCalledTimes(1);
+
+            (object as any)[field] = 100;
+            expect(setter).toBeCalledTimes(1);
+            expect(setter).lastCalledWith(100);
+        });
+    });
+});

packages/struct/src/runtime/runtime-value.ts

@@ -0,0 +1,28 @@
+import { FieldRuntimeValue } from './runtime-type';
+
+const RuntimeValues = Symbol('RuntimeValues');
+
+export interface WithRuntimeValues {
+    [RuntimeValues]: Record<string, FieldRuntimeValue>;
+}
+
+export function createObjectWithRuntimeValues(): WithRuntimeValues {
+    const object = {} as any;
+    object[RuntimeValues] = {};
+    return object;
+}
+
+export function getRuntimeValue(object: WithRuntimeValues, field: string): FieldRuntimeValue {
+    return (object as any)[RuntimeValues][field] as FieldRuntimeValue;
+}
+
+export function setRuntimeValue(object: WithRuntimeValues, field: string, runtimeValue: FieldRuntimeValue): void {
+    (object as any)[RuntimeValues][field] = runtimeValue;
+    delete (object as any)[field];
+    Object.defineProperty(object, field, {
+        configurable: true,
+        enumerable: true,
+        get() { return runtimeValue.get(); },
+        set(value) { runtimeValue.set(value); },
+    });
+}

packages/struct/src/struct.ts

@@ -1,135 +1,166 @@
-import { BackingField, defineSimpleAccessors, setBackingField, WithBackingField } from './backing-field';
+import { BuiltInFieldType, createObjectWithRuntimeValues, FieldDescriptorBase, FieldDescriptorBaseOptions, FieldRuntimeValue, getRuntimeValue, GlobalStructFieldRuntimeTypeRegistry, setRuntimeValue, StructDefaultOptions, StructDeserializationContext, StructOptions, StructSerializationContext } from './runtime';
-import { Array, FieldDescriptorBase, FieldDescriptorBaseOptions, FieldType, FieldTypeDefinition, FixedLengthArray, getFieldTypeDefinition, Number, VariableLengthArray } from './field';
+import { ArrayBufferLikeFieldDescriptor, Evaluate, FixedLengthArrayBufferFieldDescriptor, Identity, KeysOfType, NumberFieldDescriptor, NumberFieldSubType, OmitNever, Overwrite, VariableLengthArrayBufferFieldDescriptor } from './types';
-import { StructDefaultOptions, StructDeserializationContext, StructOptions, StructSerializationContext } from './types';
-import { Evaluate, Identity, OmitNever, Overwrite } from './utils';
 
+/**
+ * Extract the value type of the specified `Struct`
+ *
+ * The lack of generic constraint is on purpose to allow `StructLike` types
+ */
 export type StructValueType<T> =
     T extends { deserialize(context: StructDeserializationContext): Promise<infer R>; } ? R : never;
 
+/**
+ * Extract the init type of the specified `Struct`
+ */
 export type StructInitType<T extends Struct<object, object, object, unknown>> =
     T extends { create(value: infer R, ...args: any): any; } ? Evaluate<R> : never;
 
-interface AddArrayFieldDescriptor<
+/**
-    TResult extends object,
+ * Create a new `Struct` type with `TDescriptor` appended
-    TInit extends object,
+ */
-    TExtra extends object,
+type AddFieldDescriptor<
-    TAfterParsed
+    TValue extends object,
-    > {
-    <
-        TName extends string,
-        TType extends Array.SubType,
-        TTypeScriptType = Array.TypeScriptType<TType>
-        >(
-        name: TName,
-        type: TType,
-        options: FixedLengthArray.Options,
-        typescriptType?: () => TTypeScriptType,
-    ): MergeStruct<
-        TResult,
-        TInit,
-        TExtra,
-        TAfterParsed,
-        FixedLengthArray<
-            TName,
-            TType,
-            TTypeScriptType
-        >
-    >;
-
-    <
-        TName extends string,
-        TType extends Array.SubType,
-        TLengthField extends VariableLengthArray.KeyOfType<TInit, number | string>,
-        TEmptyBehavior extends VariableLengthArray.EmptyBehavior,
-        TTypeScriptType = VariableLengthArray.TypeScriptType<TType, TEmptyBehavior>
-        >(
-        name: TName,
-        type: TType,
-        options: VariableLengthArray.Options<TInit, TLengthField, TEmptyBehavior>,
-        typescriptType?: () => TTypeScriptType,
-    ): MergeStruct<
-        TResult,
-        TInit,
-        TExtra,
-        TAfterParsed,
-        VariableLengthArray<
-            TName,
-            TType,
-            TInit,
-            TLengthField,
-            TEmptyBehavior,
-            TTypeScriptType
-        >
-    >;
-}
-
-interface AddArraySubTypeFieldDescriptor<
-    TResult extends object,
     TInit extends object,
     TExtra extends object,
     TAfterParsed,
-    TType extends Array.SubType
+    TDescriptor extends FieldDescriptorBase> =
-    > {
-    <
-        TName extends string,
-        TTypeScriptType = Array.TypeScriptType<TType>
-        >(
-        name: TName,
-        options: FixedLengthArray.Options,
-        typescriptType?: () => TTypeScriptType,
-    ): MergeStruct<
-        TResult,
-        TInit,
-        TExtra,
-        TAfterParsed,
-        FixedLengthArray<
-            TName,
-            TType,
-            TTypeScriptType
-        >
-    >;
-
-    <
-        TName extends string,
-        TLengthField extends VariableLengthArray.KeyOfType<TInit, number | string>,
-        TEmptyBehavior extends VariableLengthArray.EmptyBehavior,
-        TTypeScriptType = VariableLengthArray.TypeScriptType<TType, TEmptyBehavior>
-        >(
-        name: TName,
-        options: VariableLengthArray.Options<TInit, TLengthField, TEmptyBehavior>,
-        _typescriptType?: TTypeScriptType,
-    ): MergeStruct<
-        TResult,
-        TInit,
-        TExtra,
-        TAfterParsed,
-        VariableLengthArray<
-            TName,
-            TType,
-            TInit,
-            TLengthField,
-            TEmptyBehavior,
-            TTypeScriptType
-        >
-    >;
-}
-
-type MergeStruct<
-    TResult extends object,
-    TInit extends object,
-    TExtra extends object,
-    TAfterParsed,
-    TDescriptor extends FieldDescriptorBase
-    > =
     Identity<Struct<
-        Evaluate<TResult & Exclude<TDescriptor['resultObject'], undefined>>,
+        // Merge two types
-        OmitNever<TInit & Exclude<TDescriptor['initObject'], undefined>>,
+        Evaluate<
+            TValue &
+            // `TDescriptor.resultObject` is optional, so remove `undefined` from its type
+            Exclude<TDescriptor['resultObject'], undefined>
+        >,
+        // `TDescriptor.initObject` signals removal of fields by setting its type to `never`
+        // I don't `Evaluate` here, because if I do, the result type will become too complex,
+        // and TypeScript will refuse to evaluate it.
+        OmitNever<
+            TInit &
+            // `TDescriptor.initObject` is optional, so remove `undefined` from its type
+            Exclude<TDescriptor['initObject'], undefined>
+        >,
         TExtra,
         TAfterParsed
     >>;
 
+/**
+ * Overload methods to add an array typed field
+ */
+interface AddArrayBufferFieldDescriptor<
+    TValue extends object,
+    TInit extends object,
+    TExtra extends object,
+    TAfterParsed
+    > {
+    /**
+     * Append a fixed-length array to the `Struct`
+     *
+     * @param name Name of the field
+     * @param type `Array.SubType.ArrayBuffer` or `Array.SubType.String`
+     * @param options Fixed-length array options
+     * @param typescriptType Type of the field in TypeScript.
+     * For example, if this field is a string, you can declare it as a string enum or literal union.
+     */
+    <
+        TName extends string,
+        TType extends ArrayBufferLikeFieldDescriptor.SubType,
+        TTypeScriptType extends ArrayBufferLikeFieldDescriptor.TypeScriptType<TType> = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>
+        >(
+        name: TName,
+        type: TType,
+        options: FixedLengthArrayBufferFieldDescriptor.Options,
+        typescriptType?: TTypeScriptType,
+    ): AddFieldDescriptor<
+        TValue,
+        TInit,
+        TExtra,
+        TAfterParsed,
+        FixedLengthArrayBufferFieldDescriptor<
+            TName,
+            TType,
+            TTypeScriptType
+        >
+    >;
+
+    /**
+     * Append a variable-length array to the `Struct`
+     */
+    <
+        TName extends string,
+        TType extends ArrayBufferLikeFieldDescriptor.SubType,
+        TLengthField extends KeysOfType<TInit, number | string>,
+        TTypeScriptType = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>
+        >(
+        name: TName,
+        type: TType,
+        options: VariableLengthArrayBufferFieldDescriptor.Options<TInit, TLengthField>,
+        typescriptType?: TTypeScriptType,
+    ): AddFieldDescriptor<
+        TValue,
+        TInit,
+        TExtra,
+        TAfterParsed,
+        VariableLengthArrayBufferFieldDescriptor<
+            TName,
+            TType,
+            TInit,
+            TLengthField,
+            TTypeScriptType
+        >
+    >;
+}
+
+interface AddArrayBufferSubTypeFieldDescriptor<
+    TResult extends object,
+    TInit extends object,
+    TExtra extends object,
+    TAfterParsed,
+    TType extends ArrayBufferLikeFieldDescriptor.SubType
+    > {
+    <
+        TName extends string,
+        TTypeScriptType = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>
+        >(
+        name: TName,
+        options: FixedLengthArrayBufferFieldDescriptor.Options,
+        typescriptType?: TTypeScriptType,
+    ): AddFieldDescriptor<
+        TResult,
+        TInit,
+        TExtra,
+        TAfterParsed,
+        FixedLengthArrayBufferFieldDescriptor<
+            TName,
+            TType,
+            TTypeScriptType
+        >
+    >;
+
+    <
+        TName extends string,
+        TLengthField extends KeysOfType<TInit, number | string>,
+        TTypeScriptType = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>
+        >(
+        name: TName,
+        options: VariableLengthArrayBufferFieldDescriptor.Options<TInit, TLengthField>,
+        _typescriptType?: TTypeScriptType,
+    ): AddFieldDescriptor<
+        TResult,
+        TInit,
+        TExtra,
+        TAfterParsed,
+        VariableLengthArrayBufferFieldDescriptor<
+            TName,
+            TType,
+            TInit,
+            TLengthField,
+            TTypeScriptType
+        >
+    >;
+}
+
 export type StructAfterParsed<TResult, TAfterParsed> =
-    (this: WithBackingField<TResult>, object: WithBackingField<TResult>) => TAfterParsed;
+    (this: TResult, object: TResult) => TAfterParsed;
 
 export default class Struct<
     TResult extends object = {},
@@ -142,19 +173,19 @@ export default class Struct<
     private _size = 0;
     public get size() { return this._size; }
 
-    private fields: FieldDescriptorBase[] = [];
+    private fieldDescriptors: FieldDescriptorBase[] = [];
 
     private _extra: PropertyDescriptorMap = {};
 
     private _afterParsed?: StructAfterParsed<any, any>;
 
-    public constructor(options: Partial<StructOptions> = StructDefaultOptions) {
+    public constructor(options?: Partial<StructOptions>) {
         this.options = { ...StructDefaultOptions, ...options };
     }
 
     private clone(): Struct<any, any, any, any> {
         const result = new Struct<any, any, any, any>(this.options);
-        result.fields = this.fields.slice();
+        result.fieldDescriptors = this.fieldDescriptors.slice();
         result._size = this._size;
         result._extra = this._extra;
         result._afterParsed = this._afterParsed;
@@ -162,13 +193,13 @@ export default class Struct<
     }
 
     public field<TDescriptor extends FieldDescriptorBase>(
-        field: TDescriptor,
+        descriptor: TDescriptor,
-    ): MergeStruct<TResult, TInit, TExtra, TAfterParsed, TDescriptor> {
+    ): AddFieldDescriptor<TResult, TInit, TExtra, TAfterParsed, TDescriptor> {
         const result = this.clone();
-        result.fields.push(field);
+        result.fieldDescriptors.push(descriptor);
 
-        const definition = getFieldTypeDefinition(field.type);
+        const Constructor = GlobalStructFieldRuntimeTypeRegistry.get(descriptor.type);
-        const size = definition.getSize({ field, options: this.options });
+        const size = Constructor.getSize(descriptor, this.options);
         result._size += size;
 
         return result;
@@ -176,16 +207,16 @@ export default class Struct<
 
     private number<
         TName extends string,
-        TSubType extends Number.SubType = Number.SubType,
+        TType extends NumberFieldSubType = NumberFieldSubType,
-        TTypeScriptType = Number.TypeScriptType<TSubType>
+        TTypeScriptType = TType['value']
     >(
         name: TName,
-        type: TSubType,
+        type: TType,
         options: FieldDescriptorBaseOptions = {},
         _typescriptType?: TTypeScriptType,
     ) {
-        return this.field<Number<TName, TSubType, TTypeScriptType>>({
+        return this.field<NumberFieldDescriptor<TName, TType, TTypeScriptType>>({
-            type: FieldType.Number,
+            type: BuiltInFieldType.Number,
             name,
             subType: type,
             options,
@@ -194,7 +225,7 @@ export default class Struct<
 
     public uint8<
         TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Uint8>
+        TTypeScriptType = (typeof NumberFieldSubType)['Uint8']['value']
     >(
         name: TName,
         options: FieldDescriptorBaseOptions = {},
@@ -202,7 +233,7 @@ export default class Struct<
     ) {
         return this.number(
             name,
-            Number.SubType.Uint8,
+            NumberFieldSubType.Uint8,
             options,
             _typescriptType
         );
@@ -210,7 +241,7 @@ export default class Struct<
 
     public uint16<
         TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Uint16>
+        TTypeScriptType = (typeof NumberFieldSubType)['Uint16']['value']
     >(
         name: TName,
         options: FieldDescriptorBaseOptions = {},
@@ -218,7 +249,7 @@ export default class Struct<
     ) {
         return this.number(
             name,
-            Number.SubType.Uint16,
+            NumberFieldSubType.Uint16,
             options,
             _typescriptType
         );
@@ -226,7 +257,7 @@ export default class Struct<
 
     public int32<
         TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Int32>
+        TTypeScriptType = (typeof NumberFieldSubType)['Int32']['value']
     >(
         name: TName,
         options: FieldDescriptorBaseOptions = {},
@@ -234,7 +265,7 @@ export default class Struct<
     ) {
         return this.number(
             name,
-            Number.SubType.Int32,
+            NumberFieldSubType.Int32,
             options,
             _typescriptType
         );
@@ -242,7 +273,23 @@ export default class Struct<
 
     public uint32<
         TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Uint32>
+        TTypeScriptType = (typeof NumberFieldSubType)['Uint32']['value']
+    >(
+        name: TName,
+        options: FieldDescriptorBaseOptions = {},
+        typescriptType?: TTypeScriptType,
+    ) {
+        return this.number(
+            name,
+            NumberFieldSubType.Uint32,
+            options,
+            typescriptType
+        );
+    }
+
+    public int64<
+        TName extends string,
+        TTypeScriptType = (typeof NumberFieldSubType)['Int64']['value']
     >(
         name: TName,
         options: FieldDescriptorBaseOptions = {},
@@ -250,7 +297,7 @@ export default class Struct<
     ) {
         return this.number(
             name,
-            Number.SubType.Uint32,
+            NumberFieldSubType.Int64,
             options,
             _typescriptType
         );
@@ -258,7 +305,7 @@ export default class Struct<
 
     public uint64<
         TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Uint64>
+        TTypeScriptType = (typeof NumberFieldSubType)['Uint64']['value']
     >(
         name: TName,
         options: FieldDescriptorBaseOptions = {},
@@ -266,43 +313,27 @@ export default class Struct<
     ) {
         return this.number(
             name,
-            Number.SubType.Uint64,
+            NumberFieldSubType.Uint64,
             options,
             _typescriptType
         );
     }
 
-    public int64<
+    private arrayBufferLike: AddArrayBufferFieldDescriptor<TResult, TInit, TExtra, TAfterParsed> = (
-        TName extends string,
-        TTypeScriptType = Number.TypeScriptType<Number.SubType.Int64>
-    >(
-        name: TName,
-        options: FieldDescriptorBaseOptions = {},
-        _typescriptType?: TTypeScriptType,
-    ) {
-        return this.number(
-            name,
-            Number.SubType.Int64,
-            options,
-            _typescriptType
-        );
-    }
-
-    private array: AddArrayFieldDescriptor<TResult, TInit, TExtra, TAfterParsed> = (
         name: string,
-        type: Array.SubType,
+        type: ArrayBufferLikeFieldDescriptor.SubType,
-        options: FixedLengthArray.Options | VariableLengthArray.Options
+        options: FixedLengthArrayBufferFieldDescriptor.Options | VariableLengthArrayBufferFieldDescriptor.Options
     ): Struct<any, any, any, any> => {
         if ('length' in options) {
-            return this.field<FixedLengthArray>({
+            return this.field<FixedLengthArrayBufferFieldDescriptor>({
-                type: FieldType.FixedLengthArray,
+                type: BuiltInFieldType.FixedLengthArrayBufferLike,
                 name,
                 subType: type,
                 options: options,
             });
         } else {
-            return this.field<VariableLengthArray>({
+            return this.field<VariableLengthArrayBufferFieldDescriptor>({
-                type: FieldType.VariableLengthArray,
+                type: BuiltInFieldType.VariableLengthArrayBufferLike,
                 name,
                 subType: type,
                 options: options,
@@ -310,30 +341,30 @@ export default class Struct<
         }
     };
 
-    public arrayBuffer: AddArraySubTypeFieldDescriptor<
+    public arrayBuffer: AddArrayBufferSubTypeFieldDescriptor<
         TResult,
         TInit,
         TExtra,
         TAfterParsed,
-        Array.SubType.ArrayBuffer
+        ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer
     > = <TName extends string>(
         name: TName,
         options: any
     ) => {
-            return this.array(name, Array.SubType.ArrayBuffer, options);
+            return this.arrayBufferLike(name, ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer, options);
         };
 
-    public string: AddArraySubTypeFieldDescriptor<
+    public string: AddArrayBufferSubTypeFieldDescriptor<
         TResult,
         TInit,
         TExtra,
         TAfterParsed,
-        Array.SubType.String
+        ArrayBufferLikeFieldDescriptor.SubType.String
     > = <TName extends string>(
         name: TName,
         options: any
     ) => {
-            return this.array(name, Array.SubType.String, options);
+            return this.arrayBufferLike(name, ArrayBufferLikeFieldDescriptor.SubType.String, options);
         };
 
     public extra<TValue extends Record<
@@ -342,7 +373,7 @@ export default class Struct<
             Exclude<keyof TValue, keyof TResult>>,
         never
     >>(
-        value: TValue & ThisType<WithBackingField<Overwrite<Overwrite<TExtra, TValue>, TResult>>>
+        value: TValue & ThisType<Overwrite<Overwrite<TExtra, TValue>, TResult>>
     ): Struct<
         TResult,
         TInit,
@@ -371,73 +402,39 @@ export default class Struct<
         return result;
     }
 
-    private initializeField(
+    private initializeObject(context: StructSerializationContext) {
-        context: StructSerializationContext,
+        const object = createObjectWithRuntimeValues();
-        field: FieldDescriptorBase,
-        fieldTypeDefinition: FieldTypeDefinition<any, any>,
-        object: any,
-        value: any,
-        extra?: any
-    ) {
-        if (fieldTypeDefinition.initialize) {
-            fieldTypeDefinition.initialize({
-                context,
-                extra,
-                field,
-                object,
-                options: this.options,
-                value,
-            });
-        } else {
-            setBackingField(object, field.name, value);
-            defineSimpleAccessors(object, field.name);
-        }
-    }
-
-    public create(init: TInit, context: StructSerializationContext): Overwrite<TExtra, TResult> {
-        const object: any = {
-            [BackingField]: {},
-        };
         Object.defineProperties(object, this._extra);
 
-        for (const field of this.fields) {
+        for (const descriptor of this.fieldDescriptors) {
-            const fieldTypeDefinition = getFieldTypeDefinition(field.type);
+            const Constructor = GlobalStructFieldRuntimeTypeRegistry.get(descriptor.type);
-            this.initializeField(
+
-                context,
+            const runtimeValue = new Constructor(descriptor, this.options, context, object);
-                field,
+            setRuntimeValue(object, descriptor.name, runtimeValue);
-                fieldTypeDefinition,
-                object,
-                (init as any)[field.name]
-            );
         }
 
         return object;
     }
 
+    public create(init: TInit, context: StructSerializationContext): Overwrite<TExtra, TResult> {
+        const object = this.initializeObject(context);
+
+        for (const { name: fieldName } of this.fieldDescriptors) {
+            const runtimeValue = getRuntimeValue(object, fieldName);
+            runtimeValue.set((init as any)[fieldName]);
+        }
+
+        return object as any;
+    }
+
     public async deserialize(
         context: StructDeserializationContext
     ): Promise<TAfterParsed extends undefined ? Overwrite<TExtra, TResult> : TAfterParsed> {
-        const object: any = {
+        const object = this.initializeObject(context);
-            [BackingField]: {},
-        };
-        Object.defineProperties(object, this._extra);
 
-        for (const field of this.fields) {
+        for (const { name: fieldName } of this.fieldDescriptors) {
-            const fieldTypeDefinition = getFieldTypeDefinition(field.type);
+            const runtimeValue = getRuntimeValue(object, fieldName);
-            const { value, extra } = await fieldTypeDefinition.deserialize({
+            await runtimeValue.deserialize(context, object);
-                context,
-                field,
-                object,
-                options: this.options,
-            });
-            this.initializeField(
-                context,
-                field,
-                fieldTypeDefinition,
-                object,
-                value,
-                extra
-            );
         }
 
         if (this._afterParsed) {
@@ -447,46 +444,30 @@ export default class Struct<
             }
         }
 
-        return object;
+        return object as any;
     }
 
     public serialize(init: TInit, context: StructSerializationContext): ArrayBuffer {
         const object = this.create(init, context) as any;
 
-        let size = this._size;
+        let structSize = 0;
-        let fieldSize: number[] = [];
+        const fieldsInfo: { runtimeValue: FieldRuntimeValue, size: number; }[] = [];
-        for (let i = 0; i < this.fields.length; i += 1) {
+
-            const field = this.fields[i];
+        for (const { name: fieldName } of this.fieldDescriptors) {
-            const type = getFieldTypeDefinition(field.type);
+            const runtimeValue = getRuntimeValue(object, fieldName);
-            if (type.getDynamicSize) {
+            const size = runtimeValue.getSize();
-                fieldSize[i] = type.getDynamicSize({
+            fieldsInfo.push({ runtimeValue, size });
-                    context,
+            structSize += size;
-                    field,
-                    object,
-                    options: this.options,
-                });
-                size += fieldSize[i];
-            } else {
-                fieldSize[i] = type.getSize({ field, options: this.options });
-            }
         }
 
-        const buffer = new ArrayBuffer(size);
+        const buffer = new ArrayBuffer(structSize);
         const dataView = new DataView(buffer);
         let offset = 0;
-        for (let i = 0; i < this.fields.length; i += 1) {
+        for (const { runtimeValue, size } of fieldsInfo) {
-            const field = this.fields[i];
+            runtimeValue.serialize(dataView, offset, context);
-            const type = getFieldTypeDefinition(field.type);
+            offset += size;
-            type.serialize({
-                context,
-                dataView,
-                field,
-                object,
-                offset,
-                options: this.options,
-            });
-            offset += fieldSize[i];
         }
+
         return buffer;
     }
 }

packages/struct/src/types.ts

@@ -1,17 +0,0 @@
-export interface StructSerializationContext {
-    encodeUtf8(input: string): ArrayBuffer;
-}
-
-export interface StructDeserializationContext extends StructSerializationContext {
-    decodeUtf8(buffer: ArrayBuffer): string;
-
-    read(length: number): ArrayBuffer | Promise<ArrayBuffer>;
-}
-
-export interface StructOptions {
-    littleEndian: boolean;
-}
-
-export const StructDefaultOptions: Readonly<StructOptions> = {
-    littleEndian: false,
-};

packages/struct/src/types/array-buffer.ts

@@ -0,0 +1,138 @@
+import { FieldDescriptorBase, FieldDescriptorBaseOptions, FieldRuntimeValue, StructDeserializationContext, StructSerializationContext } from '../runtime';
+
+export namespace ArrayBufferLikeFieldDescriptor {
+    export enum SubType {
+        ArrayBuffer,
+        Uint8ClampedArray,
+        String,
+    }
+
+    export type TypeScriptType<TType extends SubType = SubType> =
+        TType extends SubType.ArrayBuffer ? ArrayBuffer :
+        TType extends SubType.Uint8ClampedArray ? Uint8ClampedArray :
+        TType extends SubType.String ? string :
+        never;
+}
+
+export interface ArrayBufferLikeFieldDescriptor<
+    TName extends string = string,
+    TType extends ArrayBufferLikeFieldDescriptor.SubType = ArrayBufferLikeFieldDescriptor.SubType,
+    TResultObject = {},
+    TInitObject = {},
+    TOptions extends FieldDescriptorBaseOptions = FieldDescriptorBaseOptions
+    > extends FieldDescriptorBase<
+    TName,
+    TResultObject,
+    TInitObject,
+    TOptions
+    > {
+    subType: TType;
+}
+
+const EmptyArrayBuffer = new ArrayBuffer(0);
+const EmptyUint8ClampedArray = new Uint8ClampedArray(EmptyArrayBuffer);
+const EmptyString = '';
+
+export abstract class ArrayBufferLikeFieldRuntimeValue<TDescriptor extends ArrayBufferLikeFieldDescriptor>
+    extends FieldRuntimeValue<TDescriptor> {
+    protected arrayBuffer: ArrayBuffer | undefined;
+
+    protected typedArray: ArrayBufferView | undefined;
+
+    protected string: string | undefined;
+
+    protected getDeserializeSize(object: any): number {
+        return this.getSize();
+    }
+
+    public async deserialize(context: StructDeserializationContext, object: any): Promise<void> {
+        const size = this.getDeserializeSize(object);
+
+        this.arrayBuffer = undefined;
+        this.typedArray = undefined;
+        this.string = undefined;
+
+        if (size === 0) {
+            this.arrayBuffer = EmptyArrayBuffer;
+            switch (this.descriptor.subType) {
+                case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                    this.typedArray = EmptyUint8ClampedArray;
+                    break;
+                case ArrayBufferLikeFieldDescriptor.SubType.String:
+                    this.string = EmptyString;
+                    break;
+            }
+            return;
+        }
+
+        const buffer = await context.read(size);
+        switch (this.descriptor.subType) {
+            case ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer:
+                this.arrayBuffer = buffer;
+                break;
+            case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                this.arrayBuffer = buffer;
+                this.typedArray = new Uint8ClampedArray(buffer);
+                break;
+            case ArrayBufferLikeFieldDescriptor.SubType.String:
+                this.arrayBuffer = buffer;
+                this.string = context.decodeUtf8(buffer);
+                break;
+            default:
+                throw new Error('Unknown type');
+        }
+    }
+
+    public get(): unknown {
+        switch (this.descriptor.subType) {
+            case ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer:
+                return this.arrayBuffer;
+            case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                return this.typedArray;
+            case ArrayBufferLikeFieldDescriptor.SubType.String:
+                return this.string;
+            default:
+                throw new Error('Unknown type');
+        }
+    }
+
+    public set(value: unknown): void {
+        this.arrayBuffer = undefined;
+        this.typedArray = undefined;
+        this.string = undefined;
+
+        switch (this.descriptor.subType) {
+            case ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer:
+                this.arrayBuffer = value as ArrayBuffer;
+                break;
+            case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                this.typedArray = value as Uint8ClampedArray;
+                this.arrayBuffer = this.typedArray.buffer;
+                break;
+            case ArrayBufferLikeFieldDescriptor.SubType.String:
+                this.string = value as string;
+                break;
+            default:
+                throw new Error('Unknown type');
+        }
+    }
+
+    public serialize(dataView: DataView, offset: number, context: StructSerializationContext): void {
+        if (this.descriptor.subType !== ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer &&
+            !this.arrayBuffer) {
+            switch (this.descriptor.subType) {
+                case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                    this.arrayBuffer = this.typedArray!.buffer;
+                    break;
+                case ArrayBufferLikeFieldDescriptor.SubType.String:
+                    this.arrayBuffer = context.encodeUtf8(this.string!);
+                    break;
+                default:
+                    throw new Error('Unknown type');
+            }
+        }
+
+        new Uint8Array(dataView.buffer)
+            .set(new Uint8Array(this.arrayBuffer!), offset);
+    }
+}

packages/struct/src/types/fixed-length-array-buffer.ts

@@ -0,0 +1,37 @@
+import { BuiltInFieldType, FieldDescriptorBaseOptions, GlobalStructFieldRuntimeTypeRegistry } from '../runtime';
+import { ArrayBufferLikeFieldDescriptor, ArrayBufferLikeFieldRuntimeValue } from './array-buffer';
+
+export namespace FixedLengthArrayBufferFieldDescriptor {
+    export interface Options extends FieldDescriptorBaseOptions {
+        length: number;
+    }
+}
+
+export interface FixedLengthArrayBufferFieldDescriptor<
+    TName extends string = string,
+    TType extends ArrayBufferLikeFieldDescriptor.SubType = ArrayBufferLikeFieldDescriptor.SubType,
+    TTypeScriptType = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>,
+    TOptions extends FixedLengthArrayBufferFieldDescriptor.Options = FixedLengthArrayBufferFieldDescriptor.Options
+    > extends ArrayBufferLikeFieldDescriptor<
+    TName,
+    TType,
+    Record<TName, TTypeScriptType>,
+    Record<TName, TTypeScriptType>,
+    TOptions
+    > {
+    type: BuiltInFieldType.FixedLengthArrayBufferLike;
+
+    options: TOptions;
+};
+
+class FixedLengthArrayBufferFieldRuntimeValue
+    extends ArrayBufferLikeFieldRuntimeValue<FixedLengthArrayBufferFieldDescriptor>{
+    public static getSize(descriptor: FixedLengthArrayBufferFieldDescriptor) {
+        return descriptor.options.length;
+    }
+}
+
+GlobalStructFieldRuntimeTypeRegistry.register(
+    BuiltInFieldType.FixedLengthArrayBufferLike,
+    FixedLengthArrayBufferFieldRuntimeValue,
+);

packages/struct/src/types/index.ts

@@ -0,0 +1,5 @@
+export * from './array-buffer';
+export * from './fixed-length-array-buffer';
+export * from './number';
+export * from './utils';
+export * from './variable-length-array-buffer';

packages/struct/src/types/number.spec.ts

@@ -0,0 +1,115 @@
+import { StructDefaultOptions, StructDeserializationContext } from '../runtime';
+import { NumberFieldSubType, NumberFieldRuntimeValue } from './number';
+
+describe('Types', () => {
+    describe('Number', () => {
+        describe('NumberFieldSubType', () => {
+            it('Uint8 validation', () => {
+                const key = 'Uint8';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 1);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'get' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'set' + key);
+            });
+
+            it('Uint16 validation', () => {
+                const key = 'Uint16';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 2);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'get' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'set' + key);
+            });
+
+            it('Int32 validation', () => {
+                const key = 'Int32';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 4);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'get' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'set' + key);
+            });
+
+            it('Uint32 validation', () => {
+                const key = 'Uint32';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 4);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'get' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'set' + key);
+            });
+
+            it('Int64 validation', () => {
+                const key = 'Int64';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 8);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'getBig' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'setBig' + key);
+            });
+
+            it('Uint64 validation', () => {
+                const key = 'Uint64';
+                expect(NumberFieldSubType[key]).toHaveProperty('size', 8);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewGetter', 'getBig' + key);
+                expect(NumberFieldSubType[key]).toHaveProperty('dataViewSetter', 'setBig' + key);
+            });
+        });
+
+        describe('NumberFieldRuntimeValue', () => {
+            it('should deserialize Uint8', async () => {
+                const read = jest.fn((length: number) => new Uint8Array([1, 2, 3, 4]).buffer);
+                const context: StructDeserializationContext = {
+                    read,
+                    decodeUtf8(buffer) { throw new Error(''); },
+                    encodeUtf8(input) { throw new Error(''); },
+                };
+
+                const value = new NumberFieldRuntimeValue(
+                    { subType: NumberFieldSubType.Uint8 } as any,
+                    StructDefaultOptions,
+                    undefined as any,
+                    undefined as any,
+                );
+                await value.deserialize(context);
+
+                expect(value.get()).toBe(1);
+                expect(read).toBeCalledTimes(1);
+                expect(read).lastCalledWith(NumberFieldSubType.Uint8.size);
+            });
+
+            it('should deserialize Uint16', async () => {
+                const read = jest.fn((length: number) => new Uint8Array([1, 2, 3, 4]).buffer);
+                const context: StructDeserializationContext = {
+                    read,
+                    decodeUtf8(buffer) { throw new Error(''); },
+                    encodeUtf8(input) { throw new Error(''); },
+                };
+
+                const value = new NumberFieldRuntimeValue(
+                    { subType: NumberFieldSubType.Uint16 } as any,
+                    StructDefaultOptions,
+                    undefined as any,
+                    undefined as any,
+                );
+                await value.deserialize(context);
+
+                expect(value.get()).toBe((1 << 8) | 2);
+                expect(read).toBeCalledTimes(1);
+                expect(read).lastCalledWith(NumberFieldSubType.Uint16.size);
+            });
+
+            it('should deserialize Uint16LE', async () => {
+                const read = jest.fn((length: number) => new Uint8Array([1, 2, 3, 4]).buffer);
+                const context: StructDeserializationContext = {
+                    read,
+                    decodeUtf8(buffer) { throw new Error(''); },
+                    encodeUtf8(input) { throw new Error(''); },
+                };
+
+                const value = new NumberFieldRuntimeValue(
+                    { subType: NumberFieldSubType.Uint16 } as any,
+                    { ...StructDefaultOptions, littleEndian: true },
+                    undefined as any,
+                    undefined as any,
+                );
+                await value.deserialize(context);
+
+                expect(value.get()).toBe((2 << 8) | 1);
+                expect(read).toBeCalledTimes(1);
+                expect(read).lastCalledWith(NumberFieldSubType.Uint16.size);
+            });
+        });
+    });
+});

packages/struct/src/types/number.ts

@@ -0,0 +1,96 @@
+import { BuiltInFieldType, FieldDescriptorBase, FieldDescriptorBaseOptions, FieldRuntimeValue, GlobalStructFieldRuntimeTypeRegistry, StructDeserializationContext } from '../runtime';
+
+export type DataViewGetters =
+    { [TKey in keyof DataView]: TKey extends `get${string}` ? TKey : never }[keyof DataView];
+
+export type DataViewSetters =
+    { [TKey in keyof DataView]: TKey extends `set${string}` ? TKey : never }[keyof DataView];
+
+export class NumberFieldSubType<TTypeScriptType extends number | bigint = number | bigint> {
+    public static readonly Uint8 = new NumberFieldSubType<number>(1, 'getUint8', 'setUint8');
+
+    public static readonly Uint16 = new NumberFieldSubType<number>(2, 'getUint16', 'setUint16');
+
+    public static readonly Int32 = new NumberFieldSubType<number>(4, 'getInt32', 'setInt32');
+
+    public static readonly Uint32 = new NumberFieldSubType<number>(4, 'getUint32', 'setUint32');
+
+    public static readonly Int64 = new NumberFieldSubType<bigint>(8, 'getBigInt64', 'setBigInt64');
+
+    public static readonly Uint64 = new NumberFieldSubType<bigint>(8, 'getBigUint64', 'setBigUint64');
+
+    public readonly value!: TTypeScriptType;
+
+    public readonly size: number;
+
+    public readonly dataViewGetter: DataViewGetters;
+
+    public readonly dataViewSetter: DataViewSetters;
+
+    public constructor(
+        size: number,
+        dataViewGetter: DataViewGetters,
+        dataViewSetter: DataViewSetters
+    ) {
+        this.size = size;
+        this.dataViewGetter = dataViewGetter;
+        this.dataViewSetter = dataViewSetter;
+    }
+}
+
+export interface NumberFieldDescriptor<
+    TName extends string = string,
+    TSubType extends NumberFieldSubType<any> = NumberFieldSubType<any>,
+    TTypeScriptType = TSubType['value'],
+    TOptions extends FieldDescriptorBaseOptions = FieldDescriptorBaseOptions
+    > extends FieldDescriptorBase<
+    TName,
+    Record<TName, TTypeScriptType>,
+    Record<TName, TTypeScriptType>,
+    TOptions
+    > {
+    type: BuiltInFieldType.Number;
+
+    subType: TSubType;
+}
+
+export class NumberFieldRuntimeValue extends FieldRuntimeValue<NumberFieldDescriptor> {
+    public static getSize(descriptor: NumberFieldDescriptor): number {
+        return descriptor.subType.size;
+    }
+
+    protected value: number | bigint | undefined;
+
+    public async deserialize(context: StructDeserializationContext): Promise<void> {
+        const buffer = await context.read(this.getSize());
+        const view = new DataView(buffer);
+        this.value = view[this.descriptor.subType.dataViewGetter](
+            0,
+            this.options.littleEndian
+        );
+    }
+
+    public get(): unknown {
+        return this.value;
+    }
+
+    public set(value: unknown): void {
+        this.value = value as number | bigint;
+    }
+
+    public serialize(dataView: DataView, offset: number): void {
+        // `setBigInt64` requires a `bigint` while others require `number`
+        // So `dataView[DataViewSetters]` requires `bigint & number`
+        // and that is, `never`
+        (dataView[this.descriptor.subType.dataViewSetter] as any)(
+            offset,
+            this.value!,
+            this.options.littleEndian
+        );
+    }
+}
+
+GlobalStructFieldRuntimeTypeRegistry.register(
+    BuiltInFieldType.Number,
+    NumberFieldRuntimeValue,
+);

packages/struct/src/types/utils.ts

@@ -0,0 +1,47 @@
+/**
+ * When evaluating a very complex generic type alias,
+ * tell TypeScript to use `T`, instead of current type alias' name, as the result type name
+ *
+ * Example:
+ *
+ * ```ts
+ * type WithIdentity<T> = Identity<SomeType<T>>;
+ * type WithoutIdentity<T> = SomeType<T>;
+ *
+ * type WithIdentityResult = WithIdentity<number>;
+ * // Hover on this one shows `SomeType<number>`
+ *
+ * type WithoutIdentityResult = WithoutIdentity<number>;
+ * // Hover on this one shows `WithoutIdentity<number>`
+ * ```
+ */
+export type Identity<T> = T;
+
+/**
+ * Collapse an intersection type (`{ foo: string } & { bar: number }`) to a simple type (`{ foo: string, bar: number }`)
+ */
+export type Evaluate<T> = T extends infer U ? { [K in keyof U]: U[K] } : never;
+
+/**
+ * Overwrite fields in `TBase` with fields in `TNew`
+ */
+export type Overwrite<TBase extends object, TNew extends object> =
+    Evaluate<Omit<TBase, keyof TNew> & TNew>;
+
+/**
+ * Remove fields with `never` type
+ */
+export type OmitNever<T> = Pick<T, { [K in keyof T]: [T[K]] extends [never] ? never : K }[keyof T]>;
+
+/**
+ * Generates a type. Useful in generic type inference.
+ */
+export function placeholder<T>(): T {
+    return undefined as unknown as T;
+}
+
+/**
+ * Extract keys of fields in `T` that has type `TValue`
+ */
+export type KeysOfType<T, TValue> =
+    { [TKey in keyof T]: T[TKey] extends TValue ? TKey : never }[keyof T];

packages/struct/src/types/variable-length-array-buffer.ts

@@ -0,0 +1,126 @@
+import { BuiltInFieldType, FieldDescriptorBaseOptions, getRuntimeValue, GlobalStructFieldRuntimeTypeRegistry, setRuntimeValue, StructOptions, StructSerializationContext } from '../runtime';
+import { ArrayBufferLikeFieldDescriptor, ArrayBufferLikeFieldRuntimeValue } from './array-buffer';
+import { NumberFieldDescriptor, NumberFieldRuntimeValue } from './number';
+import { KeysOfType } from './utils';
+
+export namespace VariableLengthArrayBufferFieldDescriptor {
+    export interface Options<
+        TInit = object,
+        TLengthField extends KeysOfType<TInit, number | string> = any,
+        > extends FieldDescriptorBaseOptions {
+        lengthField: TLengthField;
+    }
+}
+
+export interface VariableLengthArrayBufferFieldDescriptor<
+    TName extends string = string,
+    TType extends ArrayBufferLikeFieldDescriptor.SubType = ArrayBufferLikeFieldDescriptor.SubType,
+    TInit = object,
+    TLengthField extends KeysOfType<TInit, number | string> = any,
+    TTypeScriptType = ArrayBufferLikeFieldDescriptor.TypeScriptType<TType>,
+    TOptions extends VariableLengthArrayBufferFieldDescriptor.Options<TInit, TLengthField> = VariableLengthArrayBufferFieldDescriptor.Options<TInit, TLengthField>
+    > extends ArrayBufferLikeFieldDescriptor<
+    TName,
+    TType,
+    Record<TName, TTypeScriptType>,
+    Record<TName, TTypeScriptType> & Record<TLengthField, never>,
+    TOptions
+    > {
+    type: BuiltInFieldType.VariableLengthArrayBufferLike;
+
+    options: TOptions;
+}
+
+class VariableLengthArrayBufferLengthFieldRuntimeValue extends NumberFieldRuntimeValue {
+    protected arrayBufferValue: VariableLengthArrayBufferFieldRuntimeValue;
+
+    public constructor(
+        descriptor: NumberFieldDescriptor,
+        options: Readonly<StructOptions>,
+        context: StructSerializationContext,
+        object: any,
+        arrayBufferValue: VariableLengthArrayBufferFieldRuntimeValue,
+    ) {
+        super(descriptor, options, context, object);
+        this.arrayBufferValue = arrayBufferValue;
+    }
+
+    getDeserializeSize() {
+        return this.value;
+    }
+
+    get() {
+        return this.arrayBufferValue.getSize();
+    }
+
+    set() { }
+
+    serialize(dataView: DataView, offset: number) {
+        this.value = this.get();
+        super.serialize(dataView, offset);
+    }
+}
+
+class VariableLengthArrayBufferFieldRuntimeValue
+    extends ArrayBufferLikeFieldRuntimeValue<VariableLengthArrayBufferFieldDescriptor> {
+    public static getSize() {
+        return 0;
+    }
+
+    protected length: number | undefined;
+
+    protected lengthFieldValue: VariableLengthArrayBufferLengthFieldRuntimeValue;
+
+    public constructor(
+        descriptor: VariableLengthArrayBufferFieldDescriptor,
+        options: Readonly<StructOptions>,
+        context: StructSerializationContext,
+        object: any
+    ) {
+        super(descriptor, options, context, object);
+
+        const lengthField = this.descriptor.options.lengthField;
+        const oldValue = getRuntimeValue(object, lengthField) as NumberFieldRuntimeValue;
+        this.lengthFieldValue = new VariableLengthArrayBufferLengthFieldRuntimeValue(
+            oldValue.descriptor,
+            this.options,
+            this.context,
+            object,
+            this
+        );
+        setRuntimeValue(object, lengthField, this.lengthFieldValue);
+    }
+
+    protected getDeserializeSize() {
+        const value = this.lengthFieldValue.getDeserializeSize() as number;
+        return value;
+    }
+
+    public getSize() {
+        if (this.length === undefined) {
+            switch (this.descriptor.subType) {
+                case ArrayBufferLikeFieldDescriptor.SubType.ArrayBuffer:
+                    this.length = this.arrayBuffer!.byteLength;
+                    break;
+                case ArrayBufferLikeFieldDescriptor.SubType.Uint8ClampedArray:
+                    this.length = this.typedArray!.byteLength;
+                    break;
+                case ArrayBufferLikeFieldDescriptor.SubType.String:
+                    this.arrayBuffer = this.context.encodeUtf8(this.string!);
+                    this.length = this.arrayBuffer.byteLength;
+                    break;
+            }
+        }
+        return this.length;
+    }
+
+    public set(value: unknown) {
+        super.set(value);
+        this.length = undefined;
+    }
+}
+
+GlobalStructFieldRuntimeTypeRegistry.register(
+    BuiltInFieldType.VariableLengthArrayBufferLike,
+    VariableLengthArrayBufferFieldRuntimeValue,
+);

packages/struct/src/utils.ts

@@ -1,12 +0,0 @@
-export type Identity<T> = T;
-
-export type Evaluate<T> = T extends infer U ? { [K in keyof U]: U[K] } : never;
-
-export type Overwrite<TBase extends object, TNew extends object> =
-    Evaluate<Omit<TBase, keyof TNew> & TNew>;
-
-export type OmitNever<T> = Pick<T, { [K in keyof T]: [T[K]] extends [never] ? never : K }[keyof T]>;
-
-export function placeholder<T>(): T {
-    return undefined as unknown as T;
-}

packages/struct/tsconfig.cjs.json

@@ -0,0 +1,11 @@
+{
+    "extends": "./tsconfig.esm.json",
+    "compilerOptions": {
+        "composite": false,
+        "module": "CommonJS",
+        "outDir": "cjs",
+        "declaration": false,
+        "declarationDir": null,
+        "declarationMap": false
+    }
+}

packages/struct/tsconfig.esm.json

@@ -0,0 +1,15 @@
+{
+    "extends": "../../tsconfig.base.json",
+    "compilerOptions": {
+        "rootDir": "src",
+        "outDir": "esm",
+        "declarationDir": "dts",
+        "types": [],
+    },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "src/**/*.spec.ts"
+    ]
+}

packages/struct/tsconfig.json

@@ -1,7 +1,10 @@
 {
-    "extends": "../../tsconfig.base.json",
+    "extends": "./tsconfig.esm.json",
     "compilerOptions": {
-        "outDir": "lib", //                       /* Redirect output structure to the directory. */
+        "noEmit": true,
-        "rootDir": "./src" //                    /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        "types": [
-    }
+            "jest"
+        ]
+    },
+    "exclude": []
 }

tsconfig.base.json

@@ -1,62 +1,48 @@
 {
     "compilerOptions": {
+        "composite": true,
         /* Basic Options */
-        "incremental": true, //                    /* Enable incremental compilation */
+        "target": "ES5", //                       /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
-        "target": "ES2018", //                     /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
+        "module": "ESNext", //                    /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
-        "module": "ESNext", //                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
+        "lib": [ //                               /* Specify library files to be included in the compilation. */
-        "lib": [ //                                /* Specify library files to be included in the compilation. */
             "ESNext"
         ],
-        // "allowJs": true,                        /* Allow javascript files to be compiled. */
+        "rootDir": "src",
-        // "checkJs": true,                        /* Report errors in .js files. */
+        "outDir": "esm",
-        // "jsx": "preserve",                      /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
+        "sourceMap": true,
-        "declaration": true, //                    /* Generates corresponding '.d.ts' file. */
+        "removeComments": true,
-        "declarationMap": true, //                 /* Generates a sourcemap for each corresponding '.d.ts' file. */
+        "declaration": true,
-        "sourceMap": true, //                      /* Generates corresponding '.map' file. */
+        "declarationDir": "dts",
-        // "outFile": "lib/index.js", //           /* Concatenate and emit output to single file. */
+        "declarationMap": true,
-        // "outDir": "lib",                        /* Redirect output structure to the directory. */
+        // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
-        // "rootDir": "./src", //                  /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+        // "noEmit": true,                        /* Do not emit outputs. */
-        "composite": true, //                      /* Enable project compilation */
+        "importHelpers": true, //                 /* Import emit helpers from 'tslib'. */
-        // "tsBuildInfoFile": "./",                /* Specify file to store incremental compilation information */
+        "downlevelIteration": true, //            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
-        // "removeComments": true,                 /* Do not emit comments to output. */
+        "isolatedModules": true, //               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
-        // "noEmit": true,                         /* Do not emit outputs. */
+        "skipLibCheck": true, //                  /* Skip type checking of all declaration files (*.d.ts). */
-        "importHelpers": true, //                  /* Import emit helpers from 'tslib'. */
-        // "downlevelIteration": true, //          /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
-        "isolatedModules": true, //                /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
         /* Strict Type-Checking Options */
-        "strict": true, //                         /* Enable all strict type-checking options. */
+        "strict": true, //                        /* Enable all strict type-checking options. */
-        // "noImplicitAny": true,                  /* Raise error on expressions and declarations with an implied 'any' type. */
-        // "strictNullChecks": true,               /* Enable strict null checks. */
-        // "strictFunctionTypes": true,            /* Enable strict checking of function types. */
-        // "strictBindCallApply": true,            /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
-        // "strictPropertyInitialization": true,   /* Enable strict checking of property initialization in classes. */
-        // "noImplicitThis": true,                 /* Raise error on 'this' expressions with an implied 'any' type. */
-        // "alwaysStrict": true,                   /* Parse in strict mode and emit "use strict" for each source file. */
         /* Additional Checks */
-        // "noUnusedLocals": true,                 /* Report errors on unused locals. */
+        // "noUnusedLocals": true,                /* Report errors on unused locals. */
-        // "noUnusedParameters": true,             /* Report errors on unused parameters. */
+        // "noUnusedParameters": true,            /* Report errors on unused parameters. */
-        "noImplicitReturns": true, //              /* Report error when not all code paths in function return a value. */
+        "noImplicitReturns": true, //             /* Report error when not all code paths in function return a value. */
-        "noFallthroughCasesInSwitch": true, //     /* Report errors for fallthrough cases in switch statement. */
+        "noFallthroughCasesInSwitch": true, //    /* Report errors for fallthrough cases in switch statement. */
+        "forceConsistentCasingInFileNames": true, /*	 Disallow inconsistently-cased references to the same file. */
         /* Module Resolution Options */
-        "moduleResolution": "node", //             /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
+        "moduleResolution": "node", //            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
-        // "baseUrl": "./",                        /* Base directory to resolve non-absolute module names. */
+        // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
-        // "paths": {},                            /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
+        // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
-        // "rootDirs": [],                         /* List of root folders whose combined content represents the structure of the project at runtime. */
+        // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
-        // "typeRoots": [],                        /* List of folders to include type definitions from. */
+        // "typeRoots": [],                       /* List of folders to include type definitions from. */
-        // "types": [],                            /* Type declaration files to be included in compilation. */
+        "types": [], //                           /* Type declaration files to be included in compilation. */
-        // "allowSyntheticDefaultImports": true,   /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
+        "esModuleInterop": true, //               /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
-        "esModuleInterop": true, //                /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
+        // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
-        // "preserveSymlinks": true,               /* Do not resolve the real path of symlinks. */
+        // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
-        // "allowUmdGlobalAccess": true,           /* Allow accessing UMD globals from modules. */
+    },
-        /* Source Map Options */
+    "include": [
-        // "sourceRoot": "",                       /* Specify the location where debugger should locate TypeScript files instead of source locations. */
+        "src"
-        // "mapRoot": "",                          /* Specify the location where debugger should locate map files instead of generated locations. */
+    ],
-        // "inlineSourceMap": true,                /* Emit a single file with source maps instead of having a separate file. */
+    "exclude": [
-        // "inlineSources": true,                  /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
+        "src/**/*.spec.ts"
-        /* Experimental Options */
+    ]
-        // "experimentalDecorators": true,         /* Enables experimental support for ES7 decorators. */
-        // "emitDecoratorMetadata": true,          /* Enables experimental support for emitting type metadata for decorators. */
-        /* Advanced Options */
-        "forceConsistentCasingInFileNames": true ///* Disallow inconsistently-cased references to the same file. */
-    }
 }