联合和交集的打字稿交集不出错

Question

我想要一个类型来确保对象的类型为A 或B 或A and B。但是，我认为应该失败的情况之一不是。我确定这很愚蠢，我只是还看不到它。

interface ValueSelector
{
    type: "id" | "value_string"
    value: string
}

interface TemporalSelector
{
    id: number
}

type Selector = (ValueSelector & TemporalSelector) | ValueSelector | TemporalSelector

// Should error
const e0: Selector = {}
const e1: Selector = { id: 0, value: "" }  // <-- does not error
const e2: Selector = { type: "id" }
const e3: Selector = { type: "value_string" }
const e4: Selector = { value: "" }
const e5: Selector = { value: "" }

// Should pass
const a1: Selector = { id: 0 }
const a2: Selector = { type: "id", value: "" }
const a3: Selector = { type: "value_string", value: "" }
const a4: Selector = { id: 0, type: "id", value: "" }
const a5: Selector = { id: 0, type: "value_string", value: "" }

Answer 1

e1 不会触发错误，因为 { id: 0, value: "" } 已经可以分配给 TemporalSelector，因为它只需要 id 属性。

为了使其正常工作，您可以使用StrictUnion 助手：

interface ValueSelector {
    type: "id" | "value_string"
    value: string
}

interface TemporalSelector {
    id: number
}

type UnionKeys<T> = T extends T ? keyof T : never;
type StrictUnionHelper<T, TAll> = 
    T extends any 
    ? T & Partial<Record<Exclude<UnionKeys<TAll>, keyof T>, never>> : never;

type StrictUnion<T> = StrictUnionHelper<T, T>


type Selector = (ValueSelector & TemporalSelector) | StrictUnion<ValueSelector | TemporalSelector>

// Should error
const e0: Selector = {}
const e1: Selector = { id: 0, value: "" }  // error
const e2: Selector = { type: "id" }
const e3: Selector = { type: "value_string" }
const e4: Selector = { value: "" }
const e5: Selector = { value: "" }

// Should pass
const a1: Selector = { id: 0 }
const a2: Selector = { type: "id", value: "" }
const a3: Selector = { type: "value_string", value: "" }
const a4: Selector = { id: 0, type: "id", value: "" }
const a5: Selector = { id: 0, type: "value_string", value: "" }

Playground