TypeScript通用密钥/属性类型保护

Question

我知道有一些与此相关的帖子，但是，我无法做到这一点：

我想键入保护和对象，它有一个通用的键来验证它是字典的字符串。有可能吗？

interface IDictionary<T> {
  [key: string]: T | undefined;
}

class HashArray<T, E extends keyof T & string> {
  private key: E;
  private dict: IDictionary<T>;
  private arr: T[];

  constructor(theyKey: E) {
    this.key = theyKey;
    this.dict = {};
    this.arr = [];
  }

  public push(elem: T) {
    this.arr.push(elem);

    if (this.isValidKey(elem[this.key])) this.dict[elem[this.key]] = elem; // Error
  }

  private isValidKey(key: T[E]): key is string { // Error
    return typeof key === "string";
  }
}

class Sample {
  oneKey: string = "1";
  anotherKey: number = 0;
}

const oneKey = new HashArray<Sample, 'oneKey'>('oneKey');
const secondKey = new HashArray<Sample, 'anotherKey'>('anotherKey');

oneKey.push(new Sample()); // Works
secondKey.push(new Sample()); // It should fail because anotherKey is number

沙盒

编译显示了两个错误：

类型'TE‘不能用于索引类型'IDictionary’ 类型谓词的类型必须分配给其参数的类型。输入'string‘不能指定键入'TE’

如何避免该错误而不禁用它？

Answer 1

因为您希望缩小elem的类型，所以需要传递给类型保护。另外，如果您希望T[E]类型为string keyof T & string不是这样做的，您将需要一个更复杂的映射条件类型，您可以阅读有关它的这里。

interface IDictionary<T> {
  [key: string]: T | undefined;
}
type KeyOfType<T, V> = {
    [P in keyof T]-?: T[P] extends V ? P : never
}[keyof T];
class HashArray<T, E extends KeyOfType<T, string>> {
  private key: E;
  private dict: IDictionary<T>;
  private arr: T[];

  constructor(theyKey: E) {
    this.key = theyKey;
    this.dict = {};
    this.arr = [];
  }

  public push(elem: T) {
    this.arr.push(elem);

    if (this.isValidKey(elem)) this.dict[elem[this.key]] = elem;
  }

  private isValidKey(elem: T): elem is T & Record<E, string> {
    return typeof elem[this.key] === "string";
  }
}

class Sample {
  oneKey: string = "1";
  anotherKey: number = 0;
}

const oneKey = new HashArray<Sample, "oneKey">("oneKey");
const secondKey = new HashArray<Sample, "anotherKey">("anotherKey");  // Fails here, Sample["anotherKey"] is not a string

oneKey.push(new Sample()); // Works
secondKey.push(new Sample()); 

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