Typescript：用变量中的类型参数值实例化一个泛型类答案

【问题标题】：Typescript: instantiate a generic class with the type parameter value in a variableTypescript：用变量中的类型参数值实例化一个泛型类
【发布时间】：2023-01-22 11:06:55
【问题描述】：

在 TypeScript 中，如何创建泛型类的实例？ (1) 当类型参数值在编译时已知，并且 (2) 何时将用作类型参数的类型名称作为字符串值传递？

https://jsfiddle.net/zn71am4v/

interface ITheValue {
  TheValue: string;
}

class Foo implements ITheValue {
  TheValue: string;

  constructor(val: string) {
    this.TheValue = val
  }
}

class Bar implements ITheValue {
  TheValue: string;
  constructor(val: string) {
    this.TheValue = val
  }
}

class Buz<T implements ITheValue> {
  Thing: T
  
  constructor(val: string) {
    this.T = new T(val);
  }
    
  getTheValue(): string {
    return this.Thing.TheValue;
  }
}

function run(whichOne: string, theValue: string): string {
  var f: Foo = new Foo('foo value'); // Well at least this works.
  
  // Can this be made to work? (It can in a proper language like C# :p)
  var buz = new Buz<whichOne>(theValue);

  // Even this doesn't work.
  var buz = new Buz<Foo>(theValue);

  return `The value is: ${buz.getTheValue}.`;
}

document.querySelector("#app").innerHTML = run('Foo', 'the value');

【问题讨论】：

标签： typescript typescript-generics

【解决方案1】：

首先，找一个合适的编辑器，比如https://www.typescriptlang.org/play，然后修复你的 Buz

class Buz<T extends ITheValue> {
  //        ^ not implements
  Thing: T
  
  constructor(val: string) {
    this.Thing = new T(val);
    //               ^! 'T' only refers to a type, but is being used as a value here.(2693)
  }
    
  getTheValue(): string {
    return this.Thing.TheValue;
  }
}


// This DOES work, you just got a "duplicate buz variable definition" error
var buz1 = new Buz<Foo>(theValue);

所以，错误是你没有通过T构造函数它不知道该把它带到哪里

class But<T extends ITheValue> {
  Thing: T
  constructor(TMaker: new (val: string) => T, val: string) {
    this.Thing = new TMaker(val);
  }
}

new But(Foo, 'test')

会工作正常

【讨论】：