如何在TypeScript中设置下限类型参数? [英] How to set lower-bound to type parameters in TypeScript?

问题描述

在TypeScript(我的版本:2.1.1)中，可以设置一个上限来键入这样的参数:

In TypeScript (my version: 2.1.1), it is okay to set an upper-bound to type parameters like this:

class Animal {}
class Cat extends Animal {}
class Kitten extends Cat{}

function foo<A extends Animal>(a: A) { /* */ }

如何在A上设置下限?以下代码不起作用:

How can I set a lower-bound on A? The following code does not work:

class Animal {}
class Cat extends Animal {}
class Kitten extends Cat{}

function foo<A super Kitten>(a: A) { /* */ }

这将导致编译错误.

在GitHub问题中，有人建议使用TypeScript存储库中的#13337

People in the GitHub issue #13337 of the TypeScript repo have suggested to use

function foo <X extends Y, Y>(y: Y) { /* */ }

到X的下界Y.但是，这并不涵盖我的情况，在这种情况下，X是实际类型而不是类型参数.

to lower-bound Y with X. But this does not cover my case, in which X is an actual type instead of a type parameter.

是否有关于如何将类型参数下限的任何想法?

Any thoughts on how to lower-bound a type parameter?

推荐答案

TypeScript尚不支持泛型的下限.目前正在讨论这样的建议-TypeScript开发人员不确定是否需要这样的功能.因此，我们只能等待并希望，他们将同意实施.

Lower-bound for generics is not supported by TypeScript yet. Such suggestion is currently discussed - TypeScript developers are not sure that such feature is necessary. So, we can only wait and hope, that they will agree to implement it.

在此处查看TypeScript问题跟踪器中的问题- https://github.com/Microsoft/TypeScript/issues/14520

See the issue in TypeScript issue tracker here - https://github.com/Microsoft/TypeScript/issues/14520

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