我有一个受歧视的工会，例如：
type Union = { a: "foo", b: string, c: number } | {a: "bar", b: boolean }
我需要派生一个包含所有潜在属性的类型，并分配可以在
Uniontype CollapsedUnion = {
a: "foo" | "bar",
b: string | boolean,
c: number | undefined
}
我怎样才能创建一个派生出这种折叠联合的泛型？
我需要一个支持任何规模联合体的泛型。
通过使用本机Omit
实用程序可以实现类似的行为作为副产品，但不幸的是，对我来说，它遗漏了每个工会成员中不存在的属性（不将它们计为
undefined?我找到了一个两种方式！
编辑：这是一个具有两个单独类型参数的解决方案。请参阅下方的具有单个联合类型参数的解决方案。
// The source types
type A = { a: "foo", b: string, c: number }
type B = { a: "bar", b: boolean }
// This utility lets T be indexed by any (string) key
type Indexify<T> = T & { [str: string]: undefined; }
// Where the magic happens ✨
type AllFields<T, R> = { [K in keyof (T & R) & string]: Indexify<T | R>[K] }
type Result = AllFields<A, B>
/**
* 🥳
* type Result = {
* a: "foo" | "bar";
* b: string | boolean;
* c: number | undefined;
* }
*/
如何运作
AllFields[K in keyof (T & R) & string]
意味着
KT & RTR& stringK类型表达式
Indexify<T | R>
返回
TRKKTR最后
Indexify<T | R>[K]
意味着我们通过
KKTR否则，它将回退到
[string]: undefined编辑：单个通用参数的解决方案
您指定实际上并不希望它适用于两个类型参数，而是适用于现有的联合类型，无论联合中有多少成员。
这需要血、汗和泪水，但我已经做到了。
// Magic as far as I'm concerned.
// Taken from https://stackoverflow.com/a/50375286/3229534
type UnionToIntersection<U> =
(U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never
// This utility lets T be indexed by any key
type Indexify<T> = T & { [str: string]: undefined; }
// To make a type where all values are undefined, so that in AllUnionKeys<T>
// TS doesn't remove the keys whose values are incompatible, e.g. string & number
type UndefinedVals<T> = { [K in keyof T]: undefined }
// This returns a union of all keys present across all members of the union T
type AllUnionKeys<T> = keyof UnionToIntersection<UndefinedVals<T>>
// Where the (rest of the) magic happens ✨
type AllFields<T> = { [K in AllUnionKeys<T> & string]: Indexify<T>[K] }
// The source types
type A = { a: "foo", b: string, c: number }
type B = { a: "bar", b: boolean; }
type Union = A | B
type Result = AllFields<Union>
/**
* 🥳
* type Result = {
* a: "foo" | "bar";
* b: string | boolean;
* c: number | undefined;
* }
*/
UnionToIntersection这是可行的；下面介绍了一种可能的解决方案。如果可以以更简单的方式实现它，我会很感兴趣。我添加了注释来引导您完成代码。
// an axiliary type -- we need to postpone creating a proper union, as a tuple type can be traversed recursively
// I added additional branch to make the task a bit harder / to make sure it works in a more generic case
type ProtoUnion = [{ a: "foo", b: string, c: number }, {a: "bar", b: boolean }, { c: string }]
// an axiliary type to recover proper Union
type CollapseToUnion<T extends Record<string, any>[], Acc = {}> = // starting with a tuple of records and accumulator
T extends [infer H, ...infer Rest] ? // traverse
Rest extends Record<string, any>[] ? // if still a record present
CollapseToUnion<Rest, (H | Acc)> : // recursive call: collapse as union
// in other cases return accumulator
Acc :
Acc
// union recovered
type Union = CollapseToUnion<ProtoUnion>
// this type is empty, so starting with union is _impossible_ to recover all needed keys in a generic way
type UnionKeys = keyof Union
// this type achieves what you are asking for but only for 2 types
type MergeAsValuesUnion<A, B> = { [K in (keyof A | keyof B)]:
K extends keyof A ?
K extends keyof B ? A[K] | B[K] :
A[K] | undefined :
K extends keyof B ? B[K] | undefined :
never
}
type OriginalUnionIntersected = MergeAsValuesUnion<ProtoUnion[0], ProtoUnion[1]>
/*
type OriginalUnionIntersected = {
a: "foo" | "bar";
b: string | boolean;
c: number | undefined;
}
*/
// this is works exactly the same as CollapseToUnion, but instead of reducing with |
// it uses MergeAsValuesUnion to reduce
type CollapseToIntersetion<T extends Record<string, any>[], Acc = {}> = T extends [infer H, ...infer Rest] ?
Rest extends Record<string, any>[] ?
CollapseToIntersetion<Rest, MergeAsValuesUnion<H, Acc>>
: Acc : Acc
const i: CollapseToIntersetion<ProtoUnion> = {
a: 'bar', // "bar" | "foo" | undefined
b: true, // string | boolean | undefined
c: undefined // string | number | undefined
}
CollapseToIntersetion{}| undefined// this is works exactly the same as CollapseToUnion,
// but instead of reducing with | -- it uses MergeAsValuesUnion to reduce;
// Acc = T[0] since Acc = {} would result in all values types unioned with undefined
type CollapseToIntersetion<T extends Record<string, any>[], Acc = T[0]> = T extends [infer H, ...infer Rest] ?
Rest extends Record<string, any>[] ?
CollapseToIntersetion<Rest, MergeAsValuesUnion<H, Acc>>
: Acc : Acc
这个解决方案基于阿伦的答案，递归地深度折叠联合，而不仅仅是在顶层：
export type ExtractObjects<T> = Extract<T, Record<keyof any, any>>
export type ExcludeObjects<T> = Exclude<T, Record<keyof any, any>>
export type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends (
k: infer I
) => void
? I
: never
export type Indexify<T> = T & { [str: string]: undefined }
export type AllUnionKeys<T> = keyof UnionToIntersection<{ [K in keyof T]: undefined }>
// https://stackoverflow.com/questions/65750673/collapsing-a-discriminated-union-derive-an-umbrella-type-with-all-possible-key
export type CollapseUnionOfOnlyObjects<T extends Record<keyof any, any>> = {
[K in AllUnionKeys<T> & string]: Indexify<T>[K]
}
type ExtractAndCollapseObjects<T> = CollapseUnionOfOnlyObjects<ExtractObjects<T>>
// recursive union collapse
export type CollapseUnion<T> = ExtractObjects<T> extends never
? T
:
| {
[K in keyof ExtractAndCollapseObjects<T>]: CollapseUnion<ExtractAndCollapseObjects<T>[K]>
}
| ExcludeObjects<T>
将我的版本留在这里，因为经过几次实验后发现它可以完成很多更简单：
type MergedUnion<T extends object> = {
[key in keyof T & string]: T[key];
};
不需要嵌套类型实用程序的多级层次结构。
type A = { type: "A", data: number; }
type B = { type: "B", data: string; }
type AorB = A | B;
// ^-- { type: "A", data: number; } | { type: "B", data: string; }
type AB = MergedUnion<A | B>;
// ^-- { type: "A" | "B", data: number | string; }