[英]How to implement type declaration with generics?
How can I define a function which is an implementation of a type declaration that includes generics? 如何定义一个函数,该函数是包含泛型的类型声明的实现?
Here's what I mean: 这就是我的意思:
abstract class Base {}
class Sub extends Base {}
declare type BaseFactory = <T extends Base>() => T;
let subFactory: BaseFactory = <Sub>():Sub => new Sub();
console.debug(subFactory()); // expect instance of Sub
Unfortunately, this produces the following error: 不幸的是,这会产生以下错误:
Sub is not assignable to parameter of type Base
Can this be done? 能做到吗?
/edit nevermind, it actually works in Playground . / edit没关系,它实际上可以在Playground中使用 。 Guess it's a compiler version issue
猜猜这是编译器版本问题
This works: 这有效:
declare type BaseFactory = <T extends Base>() => T;
let subFactory: BaseFactory = (): Sub => new Sub();
let a = subFactory<Sub>(); // type of a is Sub
( code in playground ) ( 操场上的代码 )
But I'd do it like this: 但我会这样做:
declare type BaseFactory<T extends Base> = () => T;
let subFactory: BaseFactory<Sub> = (): Sub => new Sub();
let a = subFactory(); // type of a is Sub
( code in playground ) ( 操场上的代码 )
If you're using typescript >= 2.3 then you can use default generics: 如果您使用的打字稿> = 2.3,则可以使用默认的泛型:
declare type BaseFactory<T extends Base = Base> = () => T;
And then you don't need to specify T
everywhere. 然后,您无需在所有地方都指定
T
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