根据判别器的子集获取判别联合的子集

Question

打字稿问题：

给定一个可区分的联合类型

interface A {
    discriminator: "A";
    data: string;
}

interface B {
    discriminator: "B";
    data: string;
}

interface C {
    discriminator: "C";
    num: number;
}

type U = A | B | C;
type Discriminator = U["discriminator"];

type AorB = SubsetOfU<"A"|"B">;

const f = (d:AorB) => d.data; // Should work

如何编写SubsetOfU以提取联合类型的子集？

当然，我不是在这里解决特定案例（可能只是A|B），而是一个更复杂的场景。

type SubsetOfU<K extends Discriminator> = ??????

Answer 1

该Extract预定义类型已经定义了你想要做什么：

type U = A | B | C;
type Discriminator = U["discriminator"];

type AorB = Extract<U, { discriminator: "A" | "B" }>;

const f = (d:AorB) => d.data;

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