打字稿推断"keys of parent"为类型

Question

如何将父项的键推断为嵌套属性的类型？

interface List {
[key:string]: Definition<keyof List>
}
interface Definition<T> {
[key:string]: Field<T>
}
type Field<T> = FieldA | FieldB<T>;
interface FieldA {
type: string
}
interface FieldB<T> {
definition: T 
}
const list:List = {
def1: {
field1: {
type: 'a'
}
},
def2: {
definition: 'def1'
// ~~~ Type 'string' is not assignable to type 'Field<never>'.
}
}

这里，definition属性的类型是never。我想成为def1 | def2。

或者更一般地获取父对象的键并将其用作类型。

游乐场链接

更简单的版本

interface List {
[key:string]:keyof List
}
const list:List = {
def1: 'def2',
// ~~~ Type 'string' is not assignable to type 'never'.
def2: 'def1'
// ~~~ Type 'string' is not assignable to type 'never'.
}

为什么keyof List属于never类型？考虑到我事先不认识钥匙，我怎么能拿到钥匙呢。

Answer 1

这是有效的，尽管它很难看；(

type List<K extends keyof any> = { [key in K]: K };
const list = new class C implements List<keyof C> {
def1: 'def2'
def2: 'def1'
def5: 'def5'
}

这不那么难看，也很管用；(

type List<T extends object> = { [key in keyof T]: keyof T }
const List = <O extends object>(o: List<O>): List<O> => o;
const list = List({
def1: 'def2',
def2: 'def1',
def5: 'def5'
});