📚 第十四章：最新特性与未来趋势

14.1 TypeScript 5.x 新特性

14.1.1 装饰器的标准化

// src/decorators/standard-decorators.ts - 标准化装饰器

// 类装饰器
function Entity(tableName: string) {
  return function <T extends { new (...args: any[]): {} }>(constructor: T) {
    return class extends constructor {
      static tableName = tableName;
      
      getTableName() {
        return tableName;
      }
    };
  };
}

// 方法装饰器
function Log(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  const originalMethod = descriptor.value;
  
  descriptor.value = function (...args: any[]) {
    console.log(`Calling ${propertyKey} with arguments:`, args);
    const result = originalMethod.apply(this, args);
    console.log(`${propertyKey} returned:`, result);
    return result;
  };
  
  return descriptor;
}

// 属性装饰器
function Column(options: ColumnOptions = {}) {
  return function (target: any, propertyKey: string) {
    const columns = Reflect.getMetadata('columns', target) || [];
    columns.push({
      propertyKey,
      ...options
    });
    Reflect.defineMetadata('columns', columns, target);
  };
}

// 参数装饰器
function Validate(validationRules: ValidationRule[]) {
  return function (target: any, propertyKey: string, parameterIndex: number) {
    const existingRules = Reflect.getMetadata('validation', target, propertyKey) || [];
    existingRules[parameterIndex] = validationRules;
    Reflect.defineMetadata('validation', existingRules, target, propertyKey);
  };
}

// 使用装饰器
@Entity('users')
class User {
  @Column({ type: 'varchar', length: 255, unique: true })
  email: string;
  
  @Column({ type: 'varchar', length: 100 })
  firstName: string;
  
  @Column({ type: 'varchar', length: 100 })
  lastName: string;
  
  @Column({ type: 'timestamp', default: 'CURRENT_TIMESTAMP' })
  createdAt: Date;
  
  constructor(email: string, firstName: string, lastName: string) {
    this.email = email;
    this.firstName = firstName;
    this.lastName = lastName;
    this.createdAt = new Date();
  }
  
  @Log
  getFullName(): string {
    return `${this.firstName} ${this.lastName}`;
  }
  
  @Log
  updateEmail(
    @Validate([{ type: 'email' }, { type: 'required' }])
    newEmail: string
  ): void {
    this.email = newEmail;
  }
}

// 装饰器工厂
function createValidationDecorator<T>(
  validator: (value: T) => boolean,
  errorMessage: string
) {
  return function (target: any, propertyKey: string) {
    const descriptor = Object.getOwnPropertyDescriptor(target, propertyKey) || {
      writable: true,
      enumerable: true,
      configurable: true
    };
    
    let value: T;
    
    descriptor.get = function () {
      return value;
    };
    
    descriptor.set = function (newValue: T) {
      if (!validator(newValue)) {
        throw new Error(errorMessage);
      }
      value = newValue;
    };
    
    Object.defineProperty(target, propertyKey, descriptor);
  };
}

// 自定义验证装饰器
const MinLength = (length: number) => 
  createValidationDecorator<string>(
    (value) => value.length >= length,
    `Value must be at least ${length} characters long`
  );

const Email = createValidationDecorator<string>(
  (value) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value),
  'Value must be a valid email address'
);

class UserProfile {
  @Email
  email: string;
  
  @MinLength(8)
  password: string;
  
  constructor(email: string, password: string) {
    this.email = email;
    this.password = password;
  }
}

// 装饰器组合
function Serializable(target: any) {
  target.prototype.toJSON = function () {
    const result: any = {};
    const columns = Reflect.getMetadata('columns', this) || [];
    
    for (const column of columns) {
      result[column.propertyKey] = this[column.propertyKey];
    }
    
    return result;
  };
  
  target.prototype.fromJSON = function (data: any) {
    const columns = Reflect.getMetadata('columns', this) || [];
    
    for (const column of columns) {
      if (data[column.propertyKey] !== undefined) {
        this[column.propertyKey] = data[column.propertyKey];
      }
    }
    
    return this;
  };
}

@Entity('products')
@Serializable
class Product {
  @Column({ type: 'uuid', primary: true })
  id: string;
  
  @Column({ type: 'varchar', length: 255 })
  name: string;
  
  @Column({ type: 'decimal', precision: 10, scale: 2 })
  price: number;
  
  @Column({ type: 'text' })
  description: string;
  
  constructor(id: string, name: string, price: number, description: string) {
    this.id = id;
    this.name = name;
    this.price = price;
    this.description = description;
  }
}

interface ColumnOptions {
  type?: string;
  length?: number;
  precision?: number;
  scale?: number;
  primary?: boolean;
  unique?: boolean;
  nullable?: boolean;
  default?: any;
}

interface ValidationRule {
  type: 'required' | 'email' | 'minLength' | 'maxLength' | 'pattern';
  value?: any;
  message?: string;
}

14.1.2 const 类型参数

// src/features/const-type-parameters.ts - const 类型参数

// 基本 const 类型参数
function createTuple<const T extends readonly unknown[]>(...args: T): T {
  return args;
}

// 推断为 readonly ["hello", "world", 42]
const tuple1 = createTuple("hello", "world", 42);

// 推断为 readonly [1, 2, 3]
const numbers = createTuple(1, 2, 3);

// 对象的 const 类型参数
function createConfig<const T>(config: T): T {
  return config;
}

// 推断为具体的字面量类型
const config = createConfig({
  apiUrl: "https://api.example.com",
  timeout: 5000,
  retries: 3,
  features: ["auth", "logging", "metrics"] as const
});

// config 的类型为：
// {
//   readonly apiUrl: "https://api.example.com";
//   readonly timeout: 5000;
//   readonly retries: 3;
//   readonly features: readonly ["auth", "logging", "metrics"];
// }

// 路由定义示例
function defineRoutes<const T extends Record<string, string>>(routes: T): T {
  return routes;
}

const routes = defineRoutes({
  home: "/",
  about: "/about",
  contact: "/contact",
  userProfile: "/user/:id",
  adminDashboard: "/admin/dashboard"
});

// 类型安全的路由访问
type RouteKeys = keyof typeof routes; // "home" | "about" | "contact" | "userProfile" | "adminDashboard"
type RouteValues = typeof routes[RouteKeys]; // "/" | "/about" | "/contact" | "/user/:id" | "/admin/dashboard"

// 状态机定义
function defineStateMachine<const T extends Record<string, Record<string, string>>>(
  states: T
): T {
  return states;
}

const userStateMachine = defineStateMachine({
  idle: {
    login: "authenticating",
    register: "registering"
  },
  authenticating: {
    success: "authenticated",
    failure: "idle"
  },
  authenticated: {
    logout: "idle",
    updateProfile: "updating"
  },
  updating: {
    success: "authenticated",
    failure: "authenticated"
  },
  registering: {
    success: "authenticated",
    failure: "idle"
  }
});

type UserStates = keyof typeof userStateMachine;
type UserActions<S extends UserStates> = keyof typeof userStateMachine[S];

// 类型安全的状态转换
function transition<S extends UserStates>(
  currentState: S,
  action: UserActions<S>
): typeof userStateMachine[S][UserActions<S>] {
  return userStateMachine[currentState][action];
}

// 使用示例
const nextState = transition("idle", "login"); // 类型为 "authenticating"

// API 端点定义
function defineAPI<const T extends Record<string, { method: string; path: string }>>(
  endpoints: T
): T {
  return endpoints;
}

const api = defineAPI({
  getUsers: { method: "GET", path: "/users" },
  createUser: { method: "POST", path: "/users" },
  updateUser: { method: "PUT", path: "/users/:id" },
  deleteUser: { method: "DELETE", path: "/users/:id" },
  getUserProfile: { method: "GET", path: "/users/:id/profile" }
});

// 类型安全的 API 客户端
class APIClient {
  async request<K extends keyof typeof api>(
    endpoint: K,
    options: {
      params?: Record<string, string>;
      body?: any;
    } = {}
  ): Promise<any> {
    const { method, path } = api[endpoint];
    
    let url = path;
    if (options.params) {
      for (const [key, value] of Object.entries(options.params)) {
        url = url.replace(`:${key}`, value);
      }
    }
    
    const response = await fetch(url, {
      method,
      headers: {
        'Content-Type': 'application/json'
      },
      body: options.body ? JSON.stringify(options.body) : undefined
    });
    
    return response.json();
  }
}

const client = new APIClient();

// 类型安全的 API 调用
client.request("getUsers");
client.request("updateUser", {
  params: { id: "123" },
  body: { name: "John Doe" }
});

// 表单验证规则
function defineValidationRules<const T extends Record<string, ValidationRule[]>>(
  rules: T
): T {
  return rules;
}

const validationRules = defineValidationRules({
  email: [
    { type: "required", message: "Email is required" },
    { type: "email", message: "Invalid email format" }
  ],
  password: [
    { type: "required", message: "Password is required" },
    { type: "minLength", value: 8, message: "Password must be at least 8 characters" }
  ],
  confirmPassword: [
    { type: "required", message: "Password confirmation is required" },
    { type: "match", field: "password", message: "Passwords do not match" }
  ]
});

type ValidationRules = typeof validationRules;
type FieldNames = keyof ValidationRules;

// 类型安全的表单验证器
class FormValidator {
  validate<F extends FieldNames>(
    field: F,
    value: any,
    formData?: Record<string, any>
  ): { isValid: boolean; errors: string[] } {
    const rules = validationRules[field];
    const errors: string[] = [];
    
    for (const rule of rules) {
      switch (rule.type) {
        case "required":
          if (!value) {
            errors.push(rule.message);
          }
          break;
        case "email":
          if (value && !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value)) {
            errors.push(rule.message);
          }
          break;
        case "minLength":
          if (value && value.length < rule.value) {
            errors.push(rule.message);
          }
          break;
        case "match":
          if (formData && value !== formData[rule.field]) {
            errors.push(rule.message);
          }
          break;
      }
    }
    
    return {
      isValid: errors.length === 0,
      errors
    };
  }
}

14.1.3 using 声明和显式资源管理

// src/features/resource-management.ts - 资源管理

// Symbol.dispose 和 Symbol.asyncDispose
interface Disposable {
  [Symbol.dispose](): void;
}

interface AsyncDisposable {
  [Symbol.asyncDispose](): Promise<void>;
}

// 文件资源管理
class FileHandle implements Disposable {
  private handle: number | null;
  
  constructor(private filename: string) {
    this.handle = this.openFile(filename);
    console.log(`File opened: ${filename}`);
  }
  
  private openFile(filename: string): number {
    // 模拟文件打开
    return Math.floor(Math.random() * 1000);
  }
  
  read(): string {
    if (!this.handle) {
      throw new Error('File is closed');
    }
    return `Content of ${this.filename}`;
  }
  
  write(data: string): void {
    if (!this.handle) {
      throw new Error('File is closed');
    }
    console.log(`Writing to ${this.filename}: ${data}`);
  }
  
  [Symbol.dispose](): void {
    if (this.handle) {
      console.log(`File closed: ${this.filename}`);
      this.handle = null;
    }
  }
}

// 数据库连接管理
class DatabaseConnection implements AsyncDisposable {
  private connection: any = null;
  private isConnected = false;
  
  constructor(private connectionString: string) {}
  
  async connect(): Promise<void> {
    if (this.isConnected) {
      return;
    }
    
    // 模拟异步连接
    await new Promise(resolve => setTimeout(resolve, 100));
    this.connection = { id: Math.random() };
    this.isConnected = true;
    console.log(`Database connected: ${this.connectionString}`);
  }
  
  async query(sql: string): Promise<any[]> {
    if (!this.isConnected) {
      throw new Error('Database not connected');
    }
    
    console.log(`Executing query: ${sql}`);
    return [{ id: 1, name: 'John' }];
  }
  
  async [Symbol.asyncDispose](): Promise<void> {
    if (this.isConnected) {
      // 模拟异步关闭
      await new Promise(resolve => setTimeout(resolve, 50));
      console.log(`Database disconnected: ${this.connectionString}`);
      this.connection = null;
      this.isConnected = false;
    }
  }
}

// HTTP 客户端资源管理
class HTTPClient implements AsyncDisposable {
  private abortController: AbortController;
  private activeRequests = new Set<Promise<any>>();
  
  constructor(private baseURL: string) {
    this.abortController = new AbortController();
    console.log(`HTTP client created for: ${baseURL}`);
  }
  
  async get(path: string): Promise<any> {
    const request = fetch(`${this.baseURL}${path}`, {
      signal: this.abortController.signal
    }).then(response => response.json());
    
    this.activeRequests.add(request);
    
    try {
      const result = await request;
      return result;
    } finally {
      this.activeRequests.delete(request);
    }
  }
  
  async post(path: string, data: any): Promise<any> {
    const request = fetch(`${this.baseURL}${path}`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(data),
      signal: this.abortController.signal
    }).then(response => response.json());
    
    this.activeRequests.add(request);
    
    try {
      const result = await request;
      return result;
    } finally {
      this.activeRequests.delete(request);
    }
  }
  
  async [Symbol.asyncDispose](): Promise<void> {
    // 取消所有活跃的请求
    this.abortController.abort();
    
    // 等待所有请求完成或被取消
    await Promise.allSettled(this.activeRequests);
    
    console.log(`HTTP client disposed for: ${this.baseURL}`);
  }
}

// 使用 using 声明进行同步资源管理
function processFile(filename: string): void {
  using file = new FileHandle(filename);
  
  // 文件会在作用域结束时自动关闭
  const content = file.read();
  file.write('Updated content');
  
  console.log('File content:', content);
  
  // 即使发生异常，文件也会被正确关闭
  if (Math.random() > 0.5) {
    throw new Error('Random error');
  }
} // file[Symbol.dispose]() 在这里自动调用

// 使用 await using 声明进行异步资源管理
async function queryDatabase(): Promise<void> {
  await using db = new DatabaseConnection('postgresql://localhost:5432/mydb');
  
  await db.connect();
  
  const users = await db.query('SELECT * FROM users');
  console.log('Users:', users);
  
  const products = await db.query('SELECT * FROM products');
  console.log('Products:', products);
  
  // 数据库连接会在作用域结束时自动关闭
} // db[Symbol.asyncDispose]() 在这里自动调用

// 多个资源的管理
async function processData(): Promise<void> {
  await using db = new DatabaseConnection('postgresql://localhost:5432/mydb');
  await using httpClient = new HTTPClient('https://api.example.com');
  
  await db.connect();
  
  // 从数据库获取数据
  const localData = await db.query('SELECT * FROM cache');
  
  // 从 API 获取数据
  const remoteData = await httpClient.get('/data');
  
  // 处理数据
  const processedData = {
    local: localData,
    remote: remoteData,
    timestamp: new Date().toISOString()
  };
  
  // 保存处理结果
  await httpClient.post('/results', processedData);
  
  console.log('Data processed successfully');
  
  // 所有资源会按照相反的顺序自动释放
  // 1. httpClient[Symbol.asyncDispose]()
  // 2. db[Symbol.asyncDispose]()
}

// 资源池管理
class ConnectionPool implements AsyncDisposable {
  private connections: DatabaseConnection[] = [];
  private availableConnections: DatabaseConnection[] = [];
  private maxConnections: number;
  
  constructor(
    private connectionString: string,
    maxConnections: number = 10
  ) {
    this.maxConnections = maxConnections;
  }
  
  async getConnection(): Promise<DatabaseConnection> {
    if (this.availableConnections.length > 0) {
      return this.availableConnections.pop()!;
    }
    
    if (this.connections.length < this.maxConnections) {
      const connection = new DatabaseConnection(this.connectionString);
      await connection.connect();
      this.connections.push(connection);
      return connection;
    }
    
    // 等待连接可用
    return new Promise((resolve) => {
      const checkForConnection = () => {
        if (this.availableConnections.length > 0) {
          resolve(this.availableConnections.pop()!);
        } else {
          setTimeout(checkForConnection, 10);
        }
      };
      checkForConnection();
    });
  }
  
  releaseConnection(connection: DatabaseConnection): void {
    this.availableConnections.push(connection);
  }
  
  async [Symbol.asyncDispose](): Promise<void> {
    // 关闭所有连接
    await Promise.all(
      this.connections.map(conn => conn[Symbol.asyncDispose]())
    );
    
    this.connections = [];
    this.availableConnections = [];
    
    console.log('Connection pool disposed');
  }
}

// 使用连接池
async function useConnectionPool(): Promise<void> {
  await using pool = new ConnectionPool('postgresql://localhost:5432/mydb', 5);
  
  // 并发查询
  const queries = Array.from({ length: 10 }, async (_, i) => {
    const connection = await pool.getConnection();
    
    try {
      const result = await connection.query(`SELECT * FROM table_${i}`);
      return result;
    } finally {
      pool.releaseConnection(connection);
    }
  });
  
  const results = await Promise.all(queries);
  console.log('All queries completed:', results.length);
  
  // 连接池会在作用域结束时自动关闭所有连接
}

// 错误处理和资源清理
async function robustResourceManagement(): Promise<void> {
  try {
    await using db = new DatabaseConnection('postgresql://localhost:5432/mydb');
    await using httpClient = new HTTPClient('https://api.example.com');
    
    await db.connect();
    
    // 模拟可能失败的操作
    if (Math.random() > 0.7) {
      throw new Error('Operation failed');
    }
    
    const data = await db.query('SELECT * FROM important_data');
    await httpClient.post('/backup', data);
    
    console.log('Backup completed successfully');
  } catch (error) {
    console.error('Operation failed:', error);
    // 即使发生错误，资源也会被正确清理
  }
  // 资源清理在这里自动进行
}

// 示例使用
async function demonstrateResourceManagement(): Promise<void> {
  console.log('=== File Processing ===');
  try {
    processFile('example.txt');
  } catch (error) {
    console.error('File processing error:', error.message);
  }
  
  console.log('\n=== Database Query ===');
  await queryDatabase();
  
  console.log('\n=== Data Processing ===');
  await processData();
  
  console.log('\n=== Connection Pool ===');
  await useConnectionPool();
  
  console.log('\n=== Robust Resource Management ===');
  await robustResourceManagement();
}

14.2 性能优化新特术

14.2.1 编译时优化

// src/optimization/compile-time.ts - 编译时优化

// 类型级别的计算
type Length<T extends readonly any[]> = T['length'];
type Head<T extends readonly any[]> = T extends readonly [infer H, ...any[]] ? H : never;
type Tail<T extends readonly any[]> = T extends readonly [any, ...infer Rest] ? Rest : [];

// 编译时字符串操作
type Split<S extends string, D extends string> = 
  S extends `${infer T}${D}${infer U}` 
    ? [T, ...Split<U, D>] 
    : [S];

type Join<T extends readonly string[], D extends string> = 
  T extends readonly [infer F, ...infer R]
    ? F extends string
      ? R extends readonly string[]
        ? R['length'] extends 0
          ? F
          : `${F}${D}${Join<R, D>}`
        : never
      : never
    : '';

// 编译时路径解析
type ParsePath<T extends string> = Split<T, '/'>;
type BuildPath<T extends readonly string[]> = Join<T, '/'>;

// 类型安全的路径构建器
class PathBuilder<T extends readonly string[] = []> {
  constructor(private segments: T) {}
  
  segment<S extends string>(segment: S): PathBuilder<[...T, S]> {
    return new PathBuilder([...this.segments, segment]);
  }
  
  build(): BuildPath<T> {
    return this.segments.join('/') as BuildPath<T>;
  }
  
  static create(): PathBuilder<[]> {
    return new PathBuilder([]);
  }
}

// 使用示例
const apiPath = PathBuilder
  .create()
  .segment('api')
  .segment('v1')
  .segment('users')
  .build(); // 类型为 "api/v1/users"

// 编译时 SQL 查询构建
type SQLSelect<T extends Record<string, any>, K extends keyof T = keyof T> = {
  select<Fields extends K[]>(...fields: Fields): SQLQuery<Pick<T, Fields[number]>>;
  where<Field extends K>(field: Field, value: T[Field]): SQLSelect<T, K>;
};

type SQLQuery<T> = {
  execute(): Promise<T[]>;
  first(): Promise<T | null>;
  count(): Promise<number>;
};

class QueryBuilder<T extends Record<string, any>> {
  private selectFields: (keyof T)[] = [];
  private whereConditions: Array<{ field: keyof T; value: any }> = [];
  
  constructor(private tableName: string) {}
  
  select<K extends keyof T>(...fields: K[]): QueryBuilder<Pick<T, K>> {
    const newBuilder = new QueryBuilder<Pick<T, K>>(this.tableName);
    newBuilder.selectFields = fields;
    newBuilder.whereConditions = this.whereConditions;
    return newBuilder;
  }
  
  where<K extends keyof T>(field: K, value: T[K]): QueryBuilder<T> {
    this.whereConditions.push({ field, value });
    return this;
  }
  
  async execute(): Promise<T[]> {
    const fields = this.selectFields.length > 0 
      ? this.selectFields.join(', ')
      : '*';
    
    let query = `SELECT ${fields} FROM ${this.tableName}`;
    
    if (this.whereConditions.length > 0) {
      const conditions = this.whereConditions
        .map(c => `${String(c.field)} = ?`)
        .join(' AND ');
      query += ` WHERE ${conditions}`;
    }
    
    console.log('Executing query:', query);
    
    // 模拟数据库查询
    return [] as T[];
  }
  
  async first(): Promise<T | null> {
    const results = await this.execute();
    return results[0] || null;
  }
  
  async count(): Promise<number> {
    // 实现计数查询
    return 0;
  }
}

// 类型安全的表定义
interface User {
  id: number;
  email: string;
  firstName: string;
  lastName: string;
  createdAt: Date;
}

interface Product {
  id: number;
  name: string;
  price: number;
  categoryId: number;
}

// 使用类型安全的查询构建器
const userQuery = new QueryBuilder<User>('users')
  .select('id', 'email', 'firstName') // 只选择指定字段
  .where('email', 'john@example.com');

// 编译时验证的配置系统
type ConfigSchema = {
  database: {
    host: string;
    port: number;
    username: string;
    password: string;
  };
  redis: {
    host: string;
    port: number;
  };
  api: {
    baseUrl: string;
    timeout: number;
    retries: number;
  };
};

type DeepKeyof<T> = {
  [K in keyof T]: T[K] extends object
    ? K | `${K & string}.${DeepKeyof<T[K]> & string}`
    : K;
}[keyof T];

type GetValueType<T, K extends string> = 
  K extends keyof T
    ? T[K]
    : K extends `${infer P}.${infer S}`
      ? P extends keyof T
        ? T[P] extends object
          ? GetValueType<T[P], S>
          : never
        : never
      : never;

class TypedConfig<T extends Record<string, any>> {
  constructor(private config: T) {}
  
  get<K extends DeepKeyof<T>>(key: K): GetValueType<T, K> {
    const keys = (key as string).split('.');
    let value: any = this.config;
    
    for (const k of keys) {
      value = value[k];
      if (value === undefined) {
        throw new Error(`Configuration key '${key}' not found`);
      }
    }
    
    return value;
  }
  
  set<K extends DeepKeyof<T>>(key: K, value: GetValueType<T, K>): void {
    const keys = (key as string).split('.');
    let target: any = this.config;
    
    for (let i = 0; i < keys.length - 1; i++) {
      target = target[keys[i]];
    }
    
    target[keys[keys.length - 1]] = value;
  }
}

const config = new TypedConfig<ConfigSchema>({
  database: {
    host: 'localhost',
    port: 5432,
    username: 'admin',
    password: 'secret'
  },
  redis: {
    host: 'localhost',
    port: 6379
  },
  api: {
    baseUrl: 'https://api.example.com',
    timeout: 5000,
    retries: 3
  }
});

// 类型安全的配置访问
const dbHost = config.get('database.host'); // string
const dbPort = config.get('database.port'); // number
const apiTimeout = config.get('api.timeout'); // number

// 编译时路由验证
type RouteParams<T extends string> = 
  T extends `${infer _Start}:${infer Param}/${infer Rest}`
    ? { [K in Param]: string } & RouteParams<Rest>
    : T extends `${infer _Start}:${infer Param}`
      ? { [K in Param]: string }
      : {};

class TypedRouter {
  private routes = new Map<string, Function>();
  
  route<T extends string>(
    path: T,
    handler: (params: RouteParams<T>) => void
  ): void {
    this.routes.set(path, handler);
  }
  
  navigate<T extends string>(
    path: T,
    params: RouteParams<T>
  ): void {
    const handler = this.routes.get(path);
    if (handler) {
      handler(params);
    }
  }
}

const router = new TypedRouter();

// 定义路由
router.route('/users/:id/posts/:postId', (params) => {
  // params 的类型为 { id: string; postId: string }
  console.log(`User ${params.id}, Post ${params.postId}`);
});

// 类型安全的导航
router.navigate('/users/:id/posts/:postId', {
  id: '123',
  postId: '456'
});

// 编译时状态管理
type StateActions<T> = {
  [K in keyof T]: (state: T, payload: any) => T;
};

class TypedStore<T extends Record<string, any>> {
  private state: T;
  private actions: StateActions<T>;
  
  constructor(initialState: T, actions: StateActions<T>) {
    this.state = initialState;
    this.actions = actions;
  }
  
  getState(): T {
    return { ...this.state };
  }
  
  dispatch<K extends keyof T>(action: K, payload: any): void {
    this.state = this.actions[action](this.state, payload);
  }
}

interface AppState {
  user: { id: string; name: string } | null;
  posts: Array<{ id: string; title: string; content: string }>;
  loading: boolean;
}

const store = new TypedStore<AppState>(
  {
    user: null,
    posts: [],
    loading: false
  },
  {
    user: (state, user) => ({ ...state, user }),
    posts: (state, posts) => ({ ...state, posts }),
    loading: (state, loading) => ({ ...state, loading })
  }
);

// 类型安全的状态更新
store.dispatch('user', { id: '1', name: 'John' });
store.dispatch('loading', true);

14.2.2 运行时优化

// src/optimization/runtime.ts - 运行时优化

// 内存池管理
class ObjectPool<T> {
  private pool: T[] = [];
  private createFn: () => T;
  private resetFn: (obj: T) => void;
  private maxSize: number;
  
  constructor(
    createFn: () => T,
    resetFn: (obj: T) => void,
    maxSize: number = 100
  ) {
    this.createFn = createFn;
    this.resetFn = resetFn;
    this.maxSize = maxSize;
  }
  
  acquire(): T {
    if (this.pool.length > 0) {
      return this.pool.pop()!;
    }
    return this.createFn();
  }
  
  release(obj: T): void {
    if (this.pool.length < this.maxSize) {
      this.resetFn(obj);
      this.pool.push(obj);
    }
  }
  
  clear(): void {
    this.pool = [];
  }
  
  get size(): number {
    return this.pool.length;
  }
}

// 示例：DOM 元素池
class DOMElementPool {
  private pools = new Map<string, ObjectPool<HTMLElement>>();
  
  getPool(tagName: string): ObjectPool<HTMLElement> {
    if (!this.pools.has(tagName)) {
      const pool = new ObjectPool<HTMLElement>(
        () => document.createElement(tagName),
        (element) => {
          element.innerHTML = '';
          element.className = '';
          element.removeAttribute('style');
          // 移除所有事件监听器
          element.replaceWith(element.cloneNode(false));
        }
      );
      this.pools.set(tagName, pool);
    }
    return this.pools.get(tagName)!;
  }
  
  createElement(tagName: string): HTMLElement {
    return this.getPool(tagName).acquire();
  }
  
  releaseElement(element: HTMLElement): void {
    const tagName = element.tagName.toLowerCase();
    const pool = this.pools.get(tagName);
    if (pool) {
      pool.release(element);
    }
  }
}

// 虚拟滚动实现
class VirtualScroller<T> {
  private container: HTMLElement;
  private items: T[];
  private itemHeight: number;
  private visibleCount: number;
  private renderItem: (item: T, index: number) => HTMLElement;
  private elementPool: DOMElementPool;
  
  private scrollTop = 0;
  private startIndex = 0;
  private endIndex = 0;
  private renderedElements: HTMLElement[] = [];
  
  constructor(options: {
    container: HTMLElement;
    items: T[];
    itemHeight: number;
    renderItem: (item: T, index: number) => HTMLElement;
  }) {
    this.container = options.container;
    this.items = options.items;
    this.itemHeight = options.itemHeight;
    this.renderItem = options.renderItem;
    this.elementPool = new DOMElementPool();
    
    this.visibleCount = Math.ceil(this.container.clientHeight / this.itemHeight) + 2;
    
    this.setupScrollListener();
    this.render();
  }
  
  private setupScrollListener(): void {
    this.container.addEventListener('scroll', () => {
      this.scrollTop = this.container.scrollTop;
      this.updateVisibleRange();
      this.render();
    });
  }
  
  private updateVisibleRange(): void {
    this.startIndex = Math.floor(this.scrollTop / this.itemHeight);
    this.endIndex = Math.min(
      this.startIndex + this.visibleCount,
      this.items.length
    );
  }
  
  private render(): void {
    // 回收当前渲染的元素
    this.renderedElements.forEach(element => {
      this.elementPool.releaseElement(element);
      element.remove();
    });
    this.renderedElements = [];
    
    // 设置容器高度
    const totalHeight = this.items.length * this.itemHeight;
    this.container.style.height = `${totalHeight}px`;
    this.container.style.position = 'relative';
    
    // 渲染可见项目
    for (let i = this.startIndex; i < this.endIndex; i++) {
      const item = this.items[i];
      const element = this.renderItem(item, i);
      
      element.style.position = 'absolute';
      element.style.top = `${i * this.itemHeight}px`;
      element.style.height = `${this.itemHeight}px`;
      
      this.container.appendChild(element);
      this.renderedElements.push(element);
    }
  }
  
  updateItems(newItems: T[]): void {
    this.items = newItems;
    this.updateVisibleRange();
    this.render();
  }
  
  scrollToIndex(index: number): void {
    const targetScrollTop = index * this.itemHeight;
    this.container.scrollTop = targetScrollTop;
  }
}

// 防抖和节流优化
class PerformanceUtils {
  static debounce<T extends (...args: any[]) => any>(
    func: T,
    delay: number
  ): (...args: Parameters<T>) => void {
    let timeoutId: NodeJS.Timeout;
    
    return (...args: Parameters<T>) => {
      clearTimeout(timeoutId);
      timeoutId = setTimeout(() => func(...args), delay);
    };
  }
  
  static throttle<T extends (...args: any[]) => any>(
    func: T,
    delay: number
  ): (...args: Parameters<T>) => void {
    let lastCall = 0;
    
    return (...args: Parameters<T>) => {
      const now = Date.now();
      if (now - lastCall >= delay) {
        lastCall = now;
        func(...args);
      }
    };
  }
  
  static memoize<T extends (...args: any[]) => any>(
    func: T,
    keyGenerator?: (...args: Parameters<T>) => string
  ): T {
    const cache = new Map<string, ReturnType<T>>();
    
    return ((...args: Parameters<T>) => {
      const key = keyGenerator ? keyGenerator(...args) : JSON.stringify(args);
      
      if (cache.has(key)) {
        return cache.get(key)!;
      }
      
      const result = func(...args);
      cache.set(key, result);
      return result;
    }) as T;
  }
  
  static requestIdleCallback(
    callback: () => void,
    options?: { timeout?: number }
  ): void {
    if ('requestIdleCallback' in window) {
      window.requestIdleCallback(callback, options);
    } else {
      // Fallback for browsers that don't support requestIdleCallback
      setTimeout(callback, 1);
    }
  }
  
  static measurePerformance<T>(
    name: string,
    fn: () => T
  ): T {
    const start = performance.now();
    const result = fn();
    const end = performance.now();
    
    console.log(`${name} took ${end - start} milliseconds`);
    return result;
  }
  
  static async measureAsyncPerformance<T>(
    name: string,
    fn: () => Promise<T>
  ): Promise<T> {
    const start = performance.now();
    const result = await fn();
    const end = performance.now();
    
    console.log(`${name} took ${end - start} milliseconds`);
    return result;
  }
}

// 批处理操作
class BatchProcessor<T> {
  private queue: T[] = [];
  private processor: (items: T[]) => Promise<void>;
  private batchSize: number;
  private delay: number;
  private timeoutId: NodeJS.Timeout | null = null;
  
  constructor(
    processor: (items: T[]) => Promise<void>,
    batchSize: number = 10,
    delay: number = 100
  ) {
    this.processor = processor;
    this.batchSize = batchSize;
    this.delay = delay;
  }
  
  add(item: T): void {
    this.queue.push(item);
    
    if (this.queue.length >= this.batchSize) {
      this.flush();
    } else if (!this.timeoutId) {
      this.timeoutId = setTimeout(() => this.flush(), this.delay);
    }
  }
  
  async flush(): Promise<void> {
    if (this.timeoutId) {
      clearTimeout(this.timeoutId);
      this.timeoutId = null;
    }
    
    if (this.queue.length === 0) {
      return;
    }
    
    const items = this.queue.splice(0, this.batchSize);
    await this.processor(items);
  }
  
  async flushAll(): Promise<void> {
    while (this.queue.length > 0) {
      await this.flush();
    }
  }
}

// 使用示例
const logBatcher = new BatchProcessor<string>(
  async (messages) => {
    console.log('Batch processing logs:', messages);
    // 批量发送到日志服务
  },
  5, // 批次大小
  1000 // 延迟时间
);

// 添加日志消息
logBatcher.add('User logged in');
logBatcher.add('User viewed profile');
logBatcher.add('User updated settings');

// 缓存管理
class LRUCache<K, V> {
  private capacity: number;
  private cache = new Map<K, V>();
  
  constructor(capacity: number) {
    this.capacity = capacity;
  }
  
  get(key: K): V | undefined {
    if (this.cache.has(key)) {
      // 移动到最后（最近使用）
      const value = this.cache.get(key)!;
      this.cache.delete(key);
      this.cache.set(key, value);
      return value;
    }
    return undefined;
  }
  
  set(key: K, value: V): void {
    if (this.cache.has(key)) {
      // 更新现有键
      this.cache.delete(key);
    } else if (this.cache.size >= this.capacity) {
      // 删除最久未使用的项目
      const firstKey = this.cache.keys().next().value;
      this.cache.delete(firstKey);
    }
    
    this.cache.set(key, value);
  }
  
  has(key: K): boolean {
    return this.cache.has(key);
  }
  
  delete(key: K): boolean {
    return this.cache.delete(key);
  }
  
  clear(): void {
    this.cache.clear();
  }
  
  get size(): number {
    return this.cache.size;
  }
}

// 异步任务队列
class TaskQueue {
  private queue: Array<() => Promise<any>> = [];
  private running = false;
  private concurrency: number;
  private activeCount = 0;
  
  constructor(concurrency: number = 1) {
    this.concurrency = concurrency;
  }
  
  add<T>(task: () => Promise<T>): Promise<T> {
    return new Promise((resolve, reject) => {
      this.queue.push(async () => {
        try {
          const result = await task();
          resolve(result);
        } catch (error) {
          reject(error);
        }
      });
      
      this.process();
    });
  }
  
  private async process(): Promise<void> {
    if (this.activeCount >= this.concurrency || this.queue.length === 0) {
      return;
    }
    
    this.activeCount++;
    const task = this.queue.shift()!;
    
    try {
      await task();
    } finally {
      this.activeCount--;
      this.process(); // 处理下一个任务
    }
  }
  
  get pending(): number {
    return this.queue.length;
  }
  
  get active(): number {
    return this.activeCount;
  }
}

// 使用示例
const taskQueue = new TaskQueue(3); // 最多同时执行3个任务

// 添加任务
for (let i = 0; i < 10; i++) {
  taskQueue.add(async () => {
    console.log(`Task ${i} started`);
    await new Promise(resolve => setTimeout(resolve, 1000));
    console.log(`Task ${i} completed`);
    return i;
  });
}

14.3 未来发展趋势

14.3.1 类型系统增强

// src/future/type-system.ts - 未来类型系统特性

// 更强大的模式匹配（概念性）
type Match<T, P extends Record<string, any>> = 
  T extends keyof P ? P[T] : never;

// 示例：状态机类型
type StateMachine = {
  idle: { start: 'running'; stop: 'idle' };
  running: { pause: 'paused'; stop: 'idle'; error: 'error' };
  paused: { resume: 'running'; stop: 'idle' };
  error: { reset: 'idle'; retry: 'running' };
};

type StateTransition<
  Current extends keyof StateMachine,
  Action extends keyof StateMachine[Current]
> = StateMachine[Current][Action];

// 类型级别的数学运算（概念性）
type Add<A extends number, B extends number> = 
  [...Array<A>, ...Array<B>]['length'];

type Subtract<A extends number, B extends number> = 
  A extends B ? 0 : never; // 简化实现

// 更精确的数组类型
type FixedArray<T, N extends number> = 
  N extends N ? number extends N ? T[] : _FixedArray<T, N, []> : never;

type _FixedArray<T, N extends number, R extends unknown[]> = 
  R['length'] extends N ? R : _FixedArray<T, N, [...R, T]>;

// 使用示例
type RGB = FixedArray<number, 3>; // [number, number, number]
type RGBA = FixedArray<number, 4>; // [number, number, number, number]

// 更强的字符串模板类型
type SQLQuery<T extends Record<string, any>> = {
  select: <K extends keyof T>(...fields: K[]) => SQLQuery<Pick<T, K>>;
  where: <K extends keyof T>(condition: `${K & string} ${ComparisonOperator} ${string}`) => SQLQuery<T>;
  orderBy: <K extends keyof T>(field: K, direction?: 'ASC' | 'DESC') => SQLQuery<T>;
  limit: (count: number) => SQLQuery<T>;
  build: () => string;
};

type ComparisonOperator = '=' | '!=' | '>' | '<' | '>=' | '<=' | 'LIKE' | 'IN';

// 高级类型推断
type InferRouteParams<T extends string> = 
  T extends `${infer Start}:${infer Param}/${infer Rest}`
    ? { [K in Param]: string } & InferRouteParams<Rest>
    : T extends `${infer Start}:${infer Param}`
      ? { [K in Param]: string }
      : {};

type InferFunctionParams<T> = 
  T extends (...args: infer P) => any ? P : never;

type InferReturnType<T> = 
  T extends (...args: any[]) => infer R ? R : never;

// 条件类型的增强
type DeepReadonly<T> = {
  readonly [P in keyof T]: T[P] extends object ? DeepReadonly<T[P]> : T[P];
};

type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends object ? DeepPartial<T[P]> : T[P];
};

type DeepRequired<T> = {
  [P in keyof T]-?: T[P] extends object ? DeepRequired<T[P]> : T[P];
};

// 类型级别的验证
type ValidateEmail<T extends string> = 
  T extends `${string}@${string}.${string}` ? T : never;

type ValidateURL<T extends string> = 
  T extends `http${'s' | ''}://${string}` ? T : never;

type ValidateUUID<T extends string> = 
  T extends `${string}-${string}-${string}-${string}-${string}` ? T : never;

// 使用示例
type MyEmail = ValidateEmail<'user@example.com'>; // 'user@example.com'
type MyURL = ValidateURL<'https://example.com'>; // 'https://example.com'
// type InvalidEmail = ValidateEmail<'invalid-email'>; // never

// 更强的映射类型
type MapToPromise<T> = {
  [K in keyof T]: Promise<T[K]>;
};

type MapToOptional<T, K extends keyof T> = {
  [P in keyof T]: P extends K ? T[P] | undefined : T[P];
};

type MapToFunction<T> = {
  [K in keyof T]: () => T[K];
};

// 类型级别的数据结构
type List<T> = {
  head: T;
  tail: List<T>;
} | null;

type Tree<T> = {
  value: T;
  left: Tree<T> | null;
  right: Tree<T> | null;
};

// 类型级别的算法（概念性）
type Reverse<T extends readonly any[]> = 
  T extends readonly [...infer Rest, infer Last]
    ? [Last, ...Reverse<Rest>]
    : [];

type Sort<T extends readonly number[]> = 
  T extends readonly [infer First, ...infer Rest]
    ? First extends number
      ? Rest extends readonly number[]
        ? [...Sort<Filter<Rest, First, 'less'>>, First, ...Sort<Filter<Rest, First, 'greater'>>]
        : [First]
      : []
    : [];

type Filter<T extends readonly number[], N extends number, Mode extends 'less' | 'greater'> = 
  T extends readonly [infer First, ...infer Rest]
    ? First extends number
      ? Rest extends readonly number[]
        ? Mode extends 'less'
          ? First extends N
            ? Filter<Rest, N, Mode>
            : [First, ...Filter<Rest, N, Mode>]
          : First extends N
            ? Filter<Rest, N, Mode>
            : [First, ...Filter<Rest, N, Mode>]
        : []
      : []
    : [];

// 更精确的错误类型
type Result<T, E = Error> = 
  | { success: true; data: T }
  | { success: false; error: E };

type AsyncResult<T, E = Error> = Promise<Result<T, E>>;

// 类型安全的错误处理
class ResultUtils {
  static ok<T>(data: T): Result<T, never> {
    return { success: true, data };
  }
  
  static err<E>(error: E): Result<never, E> {
    return { success: false, error };
  }
  
  static isOk<T, E>(result: Result<T, E>): result is { success: true; data: T } {
    return result.success;
  }
  
  static isErr<T, E>(result: Result<T, E>): result is { success: false; error: E } {
    return !result.success;
  }
  
  static map<T, U, E>(
    result: Result<T, E>,
    fn: (data: T) => U
  ): Result<U, E> {
    return result.success
      ? ResultUtils.ok(fn(result.data))
      : result;
  }
  
  static flatMap<T, U, E>(
    result: Result<T, E>,
    fn: (data: T) => Result<U, E>
  ): Result<U, E> {
    return result.success ? fn(result.data) : result;
  }
  
  static async mapAsync<T, U, E>(
    result: Result<T, E>,
    fn: (data: T) => Promise<U>
  ): Promise<Result<U, E>> {
    if (result.success) {
      try {
        const data = await fn(result.data);
        return ResultUtils.ok(data);
      } catch (error) {
        return ResultUtils.err(error as E);
      }
    }
    return result;
  }
}

// 使用示例
async function fetchUser(id: string): AsyncResult<User, string> {
  try {
    const response = await fetch(`/api/users/${id}`);
    if (!response.ok) {
      return ResultUtils.err(`HTTP ${response.status}: ${response.statusText}`);
    }
    const user = await response.json();
    return ResultUtils.ok(user);
  } catch (error) {
    return ResultUtils.err(`Network error: ${error.message}`);
  }
}

// 链式操作
async function processUser(id: string): AsyncResult<string, string> {
  const userResult = await fetchUser(id);
  
  return ResultUtils.flatMap(userResult, async (user) => {
    const profileResult = await fetchUserProfile(user.id);
    
    return ResultUtils.map(profileResult, (profile) => {
      return `${user.name} - ${profile.title}`;
    });
  });
}

14.3.2 工具链演进

// src/future/toolchain.ts - 未来工具链特性

// 更智能的类型推断
interface SmartInference {
  // 自动推断 API 响应类型
  inferAPIResponse<T extends string>(url: T): Promise<InferAPIResponseType<T>>;
  
  // 自动推断数据库查询结果类型
  inferQueryResult<T extends string>(query: T): Promise<InferQueryResultType<T>>;
  
  // 自动推断组件 Props 类型
  inferComponentProps<T extends React.ComponentType>(component: T): InferPropsType<T>;
}

// 类型级别的代码生成
type GenerateAPIClient<T extends Record<string, APIEndpoint>> = {
  [K in keyof T]: T[K] extends APIEndpoint<infer Method, infer Path, infer Params, infer Response>
    ? Method extends 'GET'
      ? (params?: Params) => Promise<Response>
      : (params: Params) => Promise<Response>
    : never;
};

interface APIEndpoint<
  Method extends string = string,
  Path extends string = string,
  Params = any,
  Response = any
> {
  method: Method;
  path: Path;
  params?: Params;
  response?: Response;
}

// 自动生成的 API 客户端
type UserAPI = {
  getUser: APIEndpoint<'GET', '/users/:id', { id: string }, User>;
  createUser: APIEndpoint<'POST', '/users', CreateUserRequest, User>;
  updateUser: APIEndpoint<'PUT', '/users/:id', { id: string } & UpdateUserRequest, User>;
  deleteUser: APIEndpoint<'DELETE', '/users/:id', { id: string }, void>;
};

type UserAPIClient = GenerateAPIClient<UserAPI>;

// 更强的开发时检查
interface DevelopmentChecks {
  // 检查未使用的导入
  checkUnusedImports(): void;
  
  // 检查循环依赖
  checkCircularDependencies(): void;
  
  // 检查性能问题
  checkPerformanceIssues(): void;
  
  // 检查安全问题
  checkSecurityIssues(): void;
}

// 智能重构工具
interface SmartRefactoring {
  // 自动提取组件
  extractComponent(selection: CodeSelection): ComponentDefinition;
  
  // 自动优化性能
  optimizePerformance(component: ComponentDefinition): ComponentDefinition;
  
  // 自动添加类型注解
  addTypeAnnotations(code: string): string;
  
  // 自动修复类型错误
  fixTypeErrors(errors: TypeError[]): CodeFix[];
}

// 增强的调试体验
interface EnhancedDebugging {
  // 类型级别的断点
  typeBreakpoint<T>(value: T): T;
  
  // 运行时类型检查
  runtimeTypeCheck<T>(value: unknown, type: TypeDefinition<T>): value is T;
  
  // 性能分析
  profileFunction<T extends (...args: any[]) => any>(fn: T): T;
  
  // 内存使用分析
  analyzeMemoryUsage(component: React.ComponentType): MemoryAnalysis;
}

14.3.3 生态系统发展

// src/future/ecosystem.ts - 生态系统发展趋势

// 更好的框架集成
interface FrameworkIntegration {
  // React 集成
  react: {
    // 自动生成 Hook 类型
    generateHookTypes<T>(hook: T): InferHookTypes<T>;
    
    // 组件类型推断
    inferComponentTypes<T extends React.ComponentType>(component: T): ComponentTypeInfo<T>;
    
    // 状态管理集成
    integrateStateManagement<T>(store: T): StateManagementTypes<T>;
  };
  
  // Vue 集成
  vue: {
    // 组合式 API 类型推断
    inferCompositionAPI<T>(setup: T): CompositionAPITypes<T>;
    
    // 模板类型检查
    checkTemplateTypes<T>(template: string, props: T): TemplateTypeCheck;
  };
  
  // Angular 集成
  angular: {
    // 依赖注入类型
    inferDITypes<T>(providers: T): DITypes<T>;
    
    // 装饰器类型推断
    inferDecoratorTypes<T>(decorator: T): DecoratorTypes<T>;
  };
}

// 更强的库类型定义
interface LibraryTypeDefinitions {
  // 自动生成类型定义
  generateTypes(library: JavaScriptLibrary): TypeDefinition;
  
  // 类型定义验证
  validateTypes(types: TypeDefinition, runtime: RuntimeBehavior): ValidationResult;
  
  // 类型定义优化
  optimizeTypes(types: TypeDefinition): OptimizedTypeDefinition;
}

// 跨平台类型支持
interface CrossPlatformTypes {
  // Node.js 特定类型
  node: {
    // 文件系统类型
    fs: FileSystemTypes;
    
    // 网络类型
    net: NetworkTypes;
    
    // 进程类型
    process: ProcessTypes;
  };
  
  // 浏览器特定类型
  browser: {
    // DOM 类型增强
    dom: EnhancedDOMTypes;
    
    // Web API 类型
    webapi: WebAPITypes;
    
    // 服务工作者类型
    serviceworker: ServiceWorkerTypes;
  };
  
  // 移动端类型
  mobile: {
    // React Native 类型
    reactnative: ReactNativeTypes;
    
    // Ionic 类型
    ionic: IonicTypes;
  };
}

// AI 辅助开发
interface AIAssistedDevelopment {
  // 代码补全增强
  enhancedCompletion: {
    // 上下文感知补全
    contextAwareCompletion(context: CodeContext): CompletionSuggestion[];
    
    // 类型驱动补全
    typeDrivenCompletion(expectedType: TypeDefinition): CompletionSuggestion[];
    
    // 模式识别补全
    patternBasedCompletion(codePattern: CodePattern): CompletionSuggestion[];
  };
  
  // 自动重构建议
  refactoringSuggestions: {
    // 性能优化建议
    performanceOptimizations(code: string): RefactoringSuggestion[];
    
    // 代码质量改进
    qualityImprovements(code: string): RefactoringSuggestion[];
    
    // 最佳实践建议
    bestPractices(code: string): BestPracticeSuggestion[];
  };
  
  // 智能错误修复
  errorFix: {
    // 自动修复类型错误
    fixTypeErrors(errors: TypeError[]): AutoFix[];
    
    // 修复运行时错误
    fixRuntimeErrors(errors: RuntimeError[]): AutoFix[];
    
    // 修复逻辑错误
    fixLogicErrors(code: string, expectedBehavior: string): AutoFix[];
  };
}

14.4 最佳实践演进

14.4.1 现代化开发流程

// src/future/modern-workflow.ts - 现代化开发流程

// 类型驱动开发
interface TypeDrivenDevelopment {
  // 先定义类型
  defineTypes(): TypeDefinitions;
  
  // 基于类型生成代码骨架
  generateCodeSkeleton(types: TypeDefinitions): CodeSkeleton;
  
  // 类型测试
  testTypes(types: TypeDefinitions): TypeTestResults;
}

// 渐进式类型采用
class ProgressiveTypeAdoption {
  // 分析现有 JavaScript 代码
  analyzeJavaScriptCode(code: string): AnalysisResult {
    return {
      complexity: this.calculateComplexity(code),
      typeableAreas: this.identifyTypeableAreas(code),
      migrationPriority: this.calculateMigrationPriority(code)
    };
  }
  
  // 生成迁移计划
  generateMigrationPlan(analysis: AnalysisResult): MigrationPlan {
    return {
      phases: this.createMigrationPhases(analysis),
      timeline: this.estimateTimeline(analysis),
      resources: this.estimateResources(analysis)
    };
  }
  
  // 自动迁移工具
  autoMigrate(code: string, options: MigrationOptions): MigrationResult {
    return {
      migratedCode: this.performMigration(code, options),
      warnings: this.generateWarnings(code),
      suggestions: this.generateSuggestions(code)
    };
  }
  
  private calculateComplexity(code: string): number {
    // 计算代码复杂度
    return 0;
  }
  
  private identifyTypeableAreas(code: string): TypeableArea[] {
    // 识别可以添加类型的区域
    return [];
  }
  
  private calculateMigrationPriority(code: string): Priority {
    // 计算迁移优先级
    return 'medium';
  }
  
  private createMigrationPhases(analysis: AnalysisResult): MigrationPhase[] {
    return [];
  }
  
  private estimateTimeline(analysis: AnalysisResult): Timeline {
    return { weeks: 4 };
  }
  
  private estimateResources(analysis: AnalysisResult): Resources {
    return { developers: 2 };
  }
  
  private performMigration(code: string, options: MigrationOptions): string {
    return code;
  }
  
  private generateWarnings(code: string): Warning[] {
    return [];
  }
  
  private generateSuggestions(code: string): Suggestion[] {
    return [];
  }
}

// 类型安全的配置管理
class TypeSafeConfiguration<T extends Record<string, any>> {
  private config: T;
  private schema: ConfigSchema<T>;
  
  constructor(config: T, schema: ConfigSchema<T>) {
    this.config = this.validateConfig(config, schema);
    this.schema = schema;
  }
  
  get<K extends keyof T>(key: K): T[K] {
    return this.config[key];
  }
  
  set<K extends keyof T>(key: K, value: T[K]): void {
    this.validateValue(key, value);
    this.config[key] = value;
  }
  
  update(updates: Partial<T>): void {
    for (const [key, value] of Object.entries(updates)) {
      this.set(key as keyof T, value);
    }
  }
  
  private validateConfig(config: T, schema: ConfigSchema<T>): T {
    // 验证配置
    return config;
  }
  
  private validateValue<K extends keyof T>(key: K, value: T[K]): void {
    // 验证单个值
  }
}

// 智能测试生成
class SmartTestGeneration {
  // 基于类型生成测试
  generateTypeBasedTests<T>(type: TypeDefinition<T>): TestSuite<T> {
    return {
      unitTests: this.generateUnitTests(type),
      integrationTests: this.generateIntegrationTests(type),
      propertyTests: this.generatePropertyTests(type)
    };
  }
  
  // 基于使用模式生成测试
  generateUsageBasedTests(usagePatterns: UsagePattern[]): TestSuite<any> {
    return {
      unitTests: [],
      integrationTests: [],
      propertyTests: []
    };
  }
  
  // 生成性能测试
  generatePerformanceTests(code: string): PerformanceTestSuite {
    return {
      benchmarks: this.generateBenchmarks(code),
      loadTests: this.generateLoadTests(code),
      memoryTests: this.generateMemoryTests(code)
    };
  }
  
  private generateUnitTests<T>(type: TypeDefinition<T>): UnitTest<T>[] {
    return [];
  }
  
  private generateIntegrationTests<T>(type: TypeDefinition<T>): IntegrationTest<T>[] {
    return [];
  }
  
  private generatePropertyTests<T>(type: TypeDefinition<T>): PropertyTest<T>[] {
    return [];
  }
  
  private generateBenchmarks(code: string): Benchmark[] {
    return [];
  }
  
  private generateLoadTests(code: string): LoadTest[] {
    return [];
  }
  
  private generateMemoryTests(code: string): MemoryTest[] {
    return [];
  }
}

// 类型定义
interface AnalysisResult {
  complexity: number;
  typeableAreas: TypeableArea[];
  migrationPriority: Priority;
}

interface TypeableArea {
  location: CodeLocation;
  type: 'function' | 'variable' | 'class' | 'interface';
  confidence: number;
}

type Priority = 'low' | 'medium' | 'high';

interface MigrationPlan {
  phases: MigrationPhase[];
  timeline: Timeline;
  resources: Resources;
}

interface MigrationPhase {
  name: string;
  description: string;
  tasks: Task[];
  duration: number;
}

interface Timeline {
  weeks: number;
}

interface Resources {
  developers: number;
}

interface MigrationOptions {
  strict: boolean;
  preserveComments: boolean;
  generateTests: boolean;
}

interface MigrationResult {
  migratedCode: string;
  warnings: Warning[];
  suggestions: Suggestion[];
}

interface Warning {
  message: string;
  location: CodeLocation;
  severity: 'low' | 'medium' | 'high';
}

interface Suggestion {
  message: string;
  location: CodeLocation;
  autoFixAvailable: boolean;
}

interface CodeLocation {
  line: number;
  column: number;
  file: string;
}

interface Task {
  name: string;
  description: string;
  estimatedHours: number;
}

interface ConfigSchema<T> {
  [K in keyof T]: {
    type: string;
    required: boolean;
    default?: T[K];
    validator?: (value: T[K]) => boolean;
  };
}

interface TestSuite<T> {
  unitTests: UnitTest<T>[];
  integrationTests: IntegrationTest<T>[];
  propertyTests: PropertyTest<T>[];
}

interface UnitTest<T> {
  name: string;
  input: any;
  expectedOutput: any;
  setup?: () => void;
  teardown?: () => void;
}

interface IntegrationTest<T> {
  name: string;
  scenario: string;
  steps: TestStep[];
}

interface PropertyTest<T> {
  name: string;
  property: (input: T) => boolean;
  generator: () => T;
}

interface TestStep {
  action: string;
  input?: any;
  expectedResult?: any;
}

interface PerformanceTestSuite {
  benchmarks: Benchmark[];
  loadTests: LoadTest[];
  memoryTests: MemoryTest[];
}

interface Benchmark {
  name: string;
  code: string;
  iterations: number;
  expectedPerformance?: PerformanceMetrics;
}

interface LoadTest {
  name: string;
  scenario: string;
  concurrency: number;
  duration: number;
}

interface MemoryTest {
  name: string;
  code: string;
  maxMemoryUsage: number;
}

interface PerformanceMetrics {
  averageTime: number;
  minTime: number;
  maxTime: number;
  memoryUsage: number;
}

interface UsagePattern {
  pattern: string;
  frequency: number;
  context: string;
}

本章练习

1. 新特性实践：

   • 使用装饰器创建一个 ORM 系统
   • 实现 const 类型参数的配置系统
   • 使用 using 声明管理资源

2. 性能优化：

   • 实现对象池和虚拟滚动
   • 创建批处理系统
   • 优化类型计算性能

3. 未来特性探索：

   • 设计更强的类型系统
   • 实现智能代码生成
   • 创建 AI 辅助开发工具

4. 现代化流程：

   • 设计渐进式迁移策略
   • 实现智能测试生成
   • 创建类型驱动开发流程

本章总结

本章介绍了 TypeScript 的最新特性和未来发展趋势：

1. TypeScript 5.x 新特性：装饰器标准化、const 类型参数、资源管理
2. 性能优化新技术：编译时优化、运行时优化
3. 未来发展趋势：类型系统增强、工具链演进、生态系统发展
4. 最佳实践演进：现代化开发流程、智能化工具

下一章将通过一个综合项目来整合所有学到的知识。