typescript - 使用泛型基于输入的窄返回类型

Question

我正在尝试使用泛型根据输入的特定形状来缩小函数的返回类型。这在 TypeScript 中甚至可能吗？我有以下 MRE 证明了这个问题:

type ValidInput = {
   filename: string;
   sender: number;
};

type ValidInput2 = {
   person: string;
   sender: string;
};

type InferSenderType<T extends { sender: any }> = T extends { sender: infer K }
  ? K
  : unknown;

type Api<I extends { sender: any }> = (input: I) => InferSenderType<I>;

declare const loadFile: Api<ValidInput | ValidInput2>;

const a = loadFile({ filename: "q", sender: 3 }); 

typeof a // string | number 

// How do I get it to narrow the return type (in this case 'number') based on the input?

Answer 1

下面是一个例子:

type ValidInput = {
   filename: string;
   sender: number;
};

type ValidInput2 = {
   person: string;
   sender: string;
};

type Api = <I extends { sender: any }>(input: I) => I['sender']

declare const loadFile: Api;

const a = loadFile({ filename: "q", sender: 3 }); 

typeof a // only number 

TS Playground