Typescript 推断的泛型类型在条件类型中未知

Question

我无法理解为什么在 createRoute 的参数中没有将 data 属性正确推断为 FeatureFlagData。基本上我想要实现的是根据 canActivate 数组中的项目(因为它实现通用 GuardWithData)。我在这里错过了什么？另外，是否有更好的方法来实现同样的目标？

下面是一些示例代码:

interface Guard {
    canActivate: () => boolean
}

export interface GuardWithData<D> extends Guard {
  data?: D;
}

export type DataType<T> = T extends GuardWithData<infer D> ? D : unknown;

class FeatureFlagGuard implements GuardWithData<FeatureFlagData> {
    canActivate() { return true; };
}

interface Route {
    canActivate: any,
    data?: object
}

interface FeatureFlagData {
    featureFlag: string;
}

type ExtractGuardData<A extends Route> = A extends {
    canActivate: GuardWithData<infer U>,
}
  ? Route & { data: U }
    : never;

function createRoute<U extends Route>(route: ExtractGuardData<U>) {
  return route;
}

createRoute({
    canActivate: FeatureFlagGuard,
    data: {} // <-- This type is to unknown, rather than the expected FeatureFlagData
})

Answer 1

interface Guard {
    canActivate: () => boolean
}

这意味着具有 canActivate 属性的对象是一个 bool 函数。您将 FeatureFlagGuard 传递给 createRoute 的方式，看起来您希望 FeatureFlagGuard 成为 bool 函数，而不是带有 的对象code>canActivate 属性。

interface Guard {
  (): boolean
}

export interface GuardWithData<D> extends Guard {
  (data?: D): boolean;
}

const FeatureFlagGuard: GuardWithData<FeatureFlagData> =
  (data?: FeatureFlagData) => true;

interface Route<D> {
  canActivate: GuardWithData<D>,
  data?: D
}

interface FeatureFlagData {
  featureFlag: string;
}

function createRoute<D>(route: Route<D>) {
  return route;
}

createRoute({
  canActivate: FeatureFlagGuard,
  data: {}
})