typescript 闭包类型推导问题 （源自koa-compose）

Question

koa-compose

koa-compose是个很有趣的洋葱型模型

import Compose from'koa-compose';

const rules =Compose([
    (ctx, next) => {
        // 下面的name怎么把ctx给推导好
        // ctx是 {name: 5}
        next();
    }
]);

rules({name: 5}, () => {
    console.log('完成');
})

ctx的类型 由 Compose返回的闭包方法传进的参数来决定, 在类型推导上有点难。。

我本来想试着用泛型, 但是泛型只能影响闭包下的

Answer 1

我帮你去翻了它的types的代码，一时我也没看懂，贴出来你参考参考，不到50行

import * as Koa from "koa";

declare function compose<T1, U1, T2, U2>(
    middleware: [Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>]
): Koa.Middleware<T1 & T2, U1 & U2>;

declare function compose<T1, U1, T2, U2, T3, U3>(
    middleware: [Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>]
): Koa.Middleware<T1 & T2 & T3, U1 & U2 & U3>;

declare function compose<T1, U1, T2, U2, T3, U3, T4, U4>(
    middleware: [Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>, Koa.Middleware<T4, U4>]
): Koa.Middleware<T1 & T2 & T3 & T4, U1 & U2 & U3 & U4>;

declare function compose<T1, U1, T2, U2, T3, U3, T4, U4, T5, U5>(
    middleware: [
        Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>, Koa.Middleware<T4, U4>,
        Koa.Middleware<T5, U5>
    ]
): Koa.Middleware<T1 & T2 & T3 & T4 & T5, U1 & U2 & U3 & U4 & U5>;

declare function compose<T1, U1, T2, U2, T3, U3, T4, U4, T5, U5, T6, U6>(
    middleware: [
        Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>, Koa.Middleware<T4, U4>,
        Koa.Middleware<T5, U5>, Koa.Middleware<T6, U6>
    ]
): Koa.Middleware<T1 & T2 & T3 & T4 & T5 & T6, U1 & U2 & U3 & U4 & U5 & U6>;

declare function compose<T1, U1, T2, U2, T3, U3, T4, U4, T5, U5, T6, U6, T7, U7>(
    middleware: [
        Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>, Koa.Middleware<T4, U4>,
        Koa.Middleware<T5, U5>, Koa.Middleware<T6, U6>, Koa.Middleware<T7, U7>
    ]
): Koa.Middleware<T1 & T2 & T3 & T4 & T5 & T6 & T7, U1 & U2 & U3 & U4 & U5 & U6 & U7>;

declare function compose<T1, U1, T2, U2, T3, U3, T4, U4, T5, U5, T6, U6, T7, U7, T8, U8>(
    middleware: [
        Koa.Middleware<T1, U1>, Koa.Middleware<T2, U2>, Koa.Middleware<T3, U3>, Koa.Middleware<T4, U4>,
        Koa.Middleware<T5, U5>, Koa.Middleware<T6, U6>, Koa.Middleware<T7, U7>, Koa.Middleware<T8, U8>
    ]
): Koa.Middleware<T1 & T2 & T3 & T4 & T5 & T6 & T7 & T8, U1 & U2 & U3 & U4 & U5 & U6 & U7 & U8>;

declare function compose<T>(middleware: Array<compose.Middleware<T>>): compose.ComposedMiddleware<T>;

declare namespace compose {
    type Middleware<T> = (context: T, next: Koa.Next) => any;
    type ComposedMiddleware<T> = (context: T, next?: Koa.Next) => Promise<void>;
}

export = compose;