TypeScript "Concreting"泛型的行为与通过值推断的泛型行为不同,

uqdfh47h 于 6个月前发布在 TypeScript

关注(0)|答案(2)|浏览(43)

Bug报告

🔎 搜索词

'T' 可以被示例化为与 'T' 无关的任意类型

🕗 版本及回归信息

在 v4.6.2 中测试

⏯ Playground链接

Playground

💻 代码

interface Monad<A> { Array: A[] }
type MonadIdentifier = keyof Monad<unknown>

declare const setBindArray:
  (bind: <A, B>(g: (a: A) => Monad<B>["Array"]) => (fa: Monad<A>["Array"]) => Monad<B>["Array"]) => void

setBindArray(g => fa => fa.flatMap(g))

declare const setBindGeneric:
  <I extends MonadIdentifier>
    ( idenfier: I
    , bind: <A, B>(g: (a: A) => Monad<B>[I]) => (fa: Monad<A>[I]) => Monad<B>[I]
    ) => void

setBindGeneric("Array", g => fa => fa.flatMap(g))
//                                 ~~~~~~~~~~~~~
// Type 'B[]' is not assignable to type 'B[]'. Two different types with this name exist, but they are unrelated.
//   Type 'B' is not assignable to type 'B'. Two different types with this name exist, but they are unrelated.
//     'B' could be instantiated with an arbitrary type which could be unrelated to 'B'.(2719)

🙁 实际行为

代码无法编译。

🙂 预期行为

代码应该可以编译。setBindArray 和 setBindGeneric 本质上是相同类型的函数，而 setBindArray 将 I 具体化为 "Array",而 setBindGeneric 通过第一个参数推断出 I 为 "Array"。

typescript

来源：https://github.com/microsoft/TypeScript/issues/48135

2条答案

按热度按时间

kr98yfug1#

最低库存：

declare const fn1:    (cb: <T>(g: () => T) => () => T) => void;
declare const fn2: <U>(cb: <T>(g: () => T) => () => T) => void;
// notice the U is a unused type parameter

fn1(g => () => g()); // OK
fn2(g => () => g()); // Error ts2719

在OP的例子中：

declare const setBindArray:
  (bind: <A, B>(g: (a: A) => Monad<B>["Array"]) => (fa: Monad<A>["Array"]) => Monad<B>["Array"]) => void

setBindArray(g => fa => fa.flatMap(g)); // OK

declare const setBindArray2:
  <T>(bind: <A, B>(g: (a: A) => Monad<B>["Array"]) => (fa: Monad<A>["Array"]) => Monad<B>["Array"]) => void

setBindArray2(g => fa => fa.flatMap(g)); // Error ts2719

赞(0）回复(0）举报 6个月前

9w11ddsr2#

我不确定这是否相关，但当我给出错误的代码时，我也收到了不正确的错误信息：

function convertToNull<T>(input: T): T {
  return input ?? null;
}

TS Playground链接
显然，由于 null 并不总是可以分配给 T,所以会出现错误 Type 'NonNullable<T> | null' is not assignable to type 'T'.,但我期望得到提示 Type 'null' is not assignable to type 'T',而我收到的是
'T' could be instantiated with an arbitrary type which could be unrelated to 'NonNullable<T> | null'