typescript - 捕获数组的类型，以便我们可以将其映射到联合类型的数组中

Question

class Custom1 { }

class Custom2 { }

class Custom3 { }

class Custom4 { }

class Foo { 
  custom1s: Custom1[];
  custom2s: Custom2[];
  custom3: Custom3;
  custom4: Custom4;
}

type SomeMapping<T> = {
  [P in keyof T]
  : T[P] extends any[] ? object[]
  : (T[P] | object);
}

type FooMapped = SomeMapping<Foo>;

实际的输入是这样的:

type FooMapped = { 
  custom1s: object[]; 
  custom2s: object[]; 
  custom3: object | Custom3; 
  custom4: object | Custom4; 
}

我想要的是:

type FooMapped = { 
  custom1s: (object | Custom1)[]; 
  custom2s: (object | Custom2)[]; 
  custom3: object | Custom3; 
  custom4: object | Custom4; 
}

我们如何捕获数组的类型以便将其转换为联合？

Answer 1

有类型

type FooMapped = { 
  custom1s: Custom1[]; 
  custom2s: Custom2[]; 
  custom3: object | Custom3; 
  custom4: object | Custom4; 
}

你应该这样做

type SomeMapping<T> = {
  [P in keyof T]
  : T[P] extends (infer U)[] ? U[]
  : (T[P] | object);
}

并实现这种类型

type FooMapped = { 
  custom1s: (object | Custom1)[]; 
  custom2s: (object | Custom2)[]; 
  custom3: object | Custom3; 
  custom4: object | Custom4; 
}

这样做

type SomeMapping<T> = {
  [P in keyof T]
  : T[P] extends (infer U)[] ? (U | object)[]
  : (T[P] | object);
}

引用:https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html (“条件类型”部分)