泛型类

类，很像接口，可以是泛型的。 当使用 new 实例化泛型类时，其类型参数的推断方式与函数调用中的方式相同：

Classes, much like interfaces, can be generic. When a generic class is instantiated with new, its type parameters are inferred the same way as in a function call:

class Box<Type> {
  contents: Type;
  constructor(value: Type) {
    this.contents = value;
  }
}

const b = new Box("hello!");
//    ^?

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