将TypeScript联合类型分解为特定类型 [英] Decompose a TypeScript union type into specific types
问题描述
我想知道是否可以将联合类型拆分"为TypeScript中的特定子类型.这是我尝试使用的代码,很明显,我正在尝试从代码片段中实现以下目标:
I wonder whether it's possible to "split" union types into the specific subtypes in TypeScript. This is the code I tried to use, it should be obvious what I'm trying to achieve from the snippet:
type SplitType<T> =
T extends (infer A)|(infer B)
? Something<A, B>
: T;
在此示例中,Something<A, B>
可以是[A, B]
,或者是完全不同的类型.这意味着SplitType<string>
只会输出string
,但是SplitType<number|string>
表示[number, string]
.
In this example Something<A, B>
could be [A, B]
, or a completely different type. This would mean that SplitType<string>
would just output a string
, but SplitType<number|string>
would mean [number, string]
.
在TypeScript中是否有可能做到这一点?如果没有的话,将来是否有一项功能可以允许这样做(例如杂色类型)?
Is something like that possible in TypeScript? And if not, is there a feature that will allow this in the future (eg. variadic types)?
推荐答案
对于固定数量的工会成员,我们可以通过生成调用签名的交集然后对其进行匹配,以单个实现定义的顺序提取工会成员.针对具有多个呼叫签名的类型.此版本仅在启用strictFunctionTypes
的情况下起作用.
For a fixed maximum number of union members, we can extract the union members in a single implementation-defined order by generating an intersection of call signatures and then matching it against a type with multiple call signatures. This version only works with strictFunctionTypes
enabled.
// https://stackoverflow.com/a/50375286
type UnionToIntersection<U> =
(U extends any ? (k: U)=>void : never) extends ((k: infer I)=>void) ? I : never
type UnionToFunctions<U> =
U extends unknown ? (k: U) => void : never;
type IntersectionOfFunctionsToType<F> =
F extends { (a: infer A): void; (b: infer B): void; (c: infer C): void; } ? [A, B, C] :
F extends { (a: infer A): void; (b: infer B): void; } ? [A, B] :
F extends { (a: infer A): void } ? [A] :
never;
type SplitType<T> =
IntersectionOfFunctionsToType<UnionToIntersection<UnionToFunctions<T>>>;
type Test1 = SplitType<number>; // [number]
type Test2 = SplitType<number | string>; // [string, number]
type Test3 = SplitType<number | string | symbol>; // [string, number, symbol]
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