FlowJS：如何使用聯合類型和布爾文字

Question

流問題似乎爭取幾個答案，但這裏有雲：

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"} : {} 
    } 
} 

最好是爲test返回值是Derived*類型之一（Return1而不是Return2），其中conditional屬性是布爾文字。

的意圖是用於流明白，如果conditional是true，則對象返回test必須含有baz，反之亦然。

這不可能嗎？

Answer 1

流量不夠聰明，無法爲您解決問題。你必須做一些事情，如：

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; 
    } 
} 

此處瞭解詳情：https://flow.org/blog/2016/07/01/New-Unions-Intersections/