流程问题似乎没有多少答案,但是可以这样:

type Base = {
  foo: string,
  bar: string
}
type Derived1 = Base & {
  conditional: false
}
type Derived2 = Base & {
  conditional: true,
  baz: string
}

type One = {
  foo: string,
  bar: string,
  conditional: boolean
}
type Two = One & {
  baz: string
}

type Return1 = Derived1 | Derived2  // fails

type Return2 = One | Two  // works, but not desired

function test(conditional: boolean): Return1 {
  return {
    foo: "foo",
    bar: "bar",
    conditional,
    ...conditional ? {baz: "baz"} : {}
  }
}


返回值test最好是Derived*类型之一(Return1而不是Return2),其中conditional属性是布尔文字。

目的是让流程理解如果conditionaltrue,则对象test返回的必须包含baz,反之亦然。

这不可能吗?

最佳答案

Flow不够智能,无法为您解决。您必须执行以下操作:

function test(conditional: boolean): Return1 {

  const base = {
    foo: "foo",
    bar: "bar",
  }

  if (!conditional) {
    return Object.assign({}, base, { conditional });
  } else {
    const result: Derived2 = Object.assign({}, base, { conditional }, {baz: "baz"});
    return result;
  }
}


此处更多信息:https://flow.org/blog/2016/07/01/New-Unions-Intersections/

10-07 21:52