typescript - 在 TypeScript 中的对象内查找类型

Question

我正在尝试在对象中引入查找类型。假设我的对象看起来像

class PersonList {
  persons = {
    john: 'description of john',
    bob: 'description of bob'
  }
}

我想要一个 getter 从 persons 中获取一个人，但没有指定 persons 对象。

文档中的getProperty

function getProperty<T, K extends keyof T>(obj: T, key: K) {
  return obj[key];  // Inferred type is T[K]
}

想要一个 obj，我想在我的 getter 中去掉它。我试过代理 setter/getter ，但没有成功:

class PersonList {
  persons = {
    john: 'description of john',
    bob: 'description of bob'
  };

  getPerson(name) {
    return this.getProperty(this.persons, name);
  }

  private getProperty<T, K extends keyof T>(obj: T, key: K) {
    return obj[key];  // Inferred type is T[K]
  }
}

遗憾的是，当尝试执行诸如 personList.getPerson('someonenotincluded'); 之类的操作时，这不会引发错误 - 此外，自动完成功能也不起作用。

Answer 1

我会采用该内联类型并为其命名(但请继续阅读，您不必):

interface Persons {
  john: string;
  bob: string;
}

然后你可以使用keyof Persons作为getPerson中的参数类型:

class PersonList {
  persons: Persons = {
    john: 'description of john',
    bob: 'description of bob'
  };

  getPerson(name: keyof Persons) {
    return this.persons[name];
  }
}

那么如果 pl 是一个 PersonList:

console.log(pl.getPerson('john')); // Works
console.log(pl.getPerson('someonenotincluded')); // Error

Live on the playground .

但是，如果您希望保持内联，您可以使用 keyof PersonList['persons'] 作为参数类型:

class PersonList {
  persons = {
    john: 'description of john',
    bob: 'description of bob'
  };

  getPerson(name: keyof PersonList['persons']) {
    return this.persons[name];
  }
}

Live on the playground .

---

在您提出的评论中:

is it possible to implement this in an abstract class? ... it would be awesome to implement the getter in the abstract class, but I haven't found a solution so far.

...带有此代码模板的链接:

abstract class AbstractPersonList {
  protected abstract persons: { [name: string]: string };
}

class Persons extends AbstractPersonList {
  persons = {
    john: 'this is john',
  }
}

class MorePersons extends AbstractPersonList {
  persons = {
    bob: 'this is bob',
  }
}

您可以参数化AbstractPersonList:

abstract class AbstractPersonList<T extends {[name: string]: string}> {
// ------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  protected abstract persons: T;
  public getPerson(name: keyof T): string {
    return this.persons[name];
  }
}

然后你会:

class Persons extends AbstractPersonList<{john: string}> {
// -------------------------------------^^^^^^^^^^^^^^^^
  persons = {
    john: 'this is john',
  }
}

class MorePersons extends AbstractPersonList<{bob: string}> {
// -----------------------------------------^^^^^^^^^^^^^^^
  persons = {
    bob: 'this is bob',
  }
}

这导致了这些结果，我认为这就是您正在寻找的:

let n = Math.random() < 0.5 ? 'john' : 'bob';

const p = new Persons();
console.log(p.getPerson('john'));  // Works
console.log(p.getPerson('bob'));   // FAILS: Argument of type '"bob"' is not assignable to parameter of type '"john"'.
console.log(p.getPerson(n));       // FAILS: Argument of type 'string' is not assignable to parameter of type '"john"'.

const mp = new MorePersons();
console.log(mp.getPerson('john')); // FAILS: Argument of type '"john"' is not assignable to parameter of type '"bob"'.
console.log(mp.getPerson('bob'));  // Works
console.log(mp.getPerson(n));      // FAILS: Argument of type 'string' is not assignable to parameter of type '"bob"'.

Live on the playground .