Question

在typescript中，我们可以使用这样的索引类型：

interface Dummy {
    name: string;
    birth: Date;
}

function doSomethingOnProperty<T, K extends keyof T>(o: T, name: K): void {
    o[name]; // do something, o[name] is of type T[K]
}

var dummy = { name: "d", birth: new Date() };

doSomethingOnProperty(dummy, "name");

问题：

如何添加通用约束以仅接受某种类型的属性名称（是否可能？）：

// Generic constraint on T[K] ? T[K] must be of type Date
function doSomethingOnDATEProperty<T, K extends keyof T>(o: T, name: K): void {
    o[name];
}

// should not compile,
// should accept only the name of propery "birth" which is of type date
doSomethingOnDATEProperty(dummy, "name");

Answer 1

您可以执行以下操作：

function doSomethingOnDATEProperty<T extends { [P in K]: Date }, K extends keyof T>(o: T, name: K): void {
    let d = o[name]; // do something, o[name] is of type T[K] but also Date
    d.getFullYear(); // Valid
}

var dummy = { name: "d", birth: new Date() };

doSomethingOnDATEProperty(dummy, "birth");

TypeScript索引类型，如何在T [K]上添加约束

1 个答案: