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Traverse the type of an object tree, find leafs that are function types and collect the type of their first argument.
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class C {} | |
const obj = { | |
a: { | |
x: { | |
y: () => 1 | |
} | |
}, | |
b: { | |
c: ({b}: { b: boolean }) => b // { b: boolean } | |
}, | |
c: () => new C(), | |
n: ({n}: { n: number }) => n, // { n: number } | |
s: ({s}: { s: string }) => s, // { s: string } | |
xxx: ({b}: { b: string }) => b // { b: string } | |
} | |
// ✅ | |
// type Test = { | |
// b: never, // <-- merge conflict, { b: boolean } & { b: string } = { b: never } | |
// n: number, | |
// s: string | |
// } | |
type Test = Reflect<typeof obj>; |
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type Reflect<T> = T extends Record<PropertyKey, unknown> | |
? MergeObjects<FunctionArgs<PickByValue<T, (...args: any[]) => any>>, Reflect<UnionToIntersection<Values<PickByValue<T, Record<PropertyKey, unknown>>>>>> | |
: unknown; | |
type Merge<S, T> = | |
Or<Is<S, never>, Is<T, never>> extends true ? never : | |
Or<Is<S, any>, Is<T, any>> extends true ? any : | |
Or<Is<S, unknown>, Is<T, unknown>> extends true ? unknown : | |
S extends Record<PropertyKey, unknown> | |
? T extends Record<PropertyKey, unknown> ? MergeObjects<S, T> : never | |
: T extends Record<PropertyKey, unknown> ? never : (S extends T ? S : never); | |
type MergeObjects<S, T> = | |
Union<{ | |
[K in keyof S | keyof T]: K extends keyof S | |
? (K extends keyof T ? Merge<S[K], T[K]> : S[K]) | |
: (K extends keyof T ? T[K] : never) | |
}>; | |
type Is<T1, T2> = (<T>() => T extends T2 ? true : false) extends <T>() => T extends T1 ? true : false ? true : false; | |
type Or<C1 extends boolean, C2 extends boolean> = C1 extends true ? true : C2 extends true ? true : false; | |
type FunctionArgs<T> = T[keyof T] extends (arg0: infer A) => any ? A : never; | |
type PickByValue<T, V> = Pick<T, { [K in keyof T]-?: T[K] extends V ? K : never }[keyof T]>; | |
type Union<T> = T extends Record<PropertyKey, unknown> ? { [K in keyof T]: T[K] } : T; | |
type UnionToIntersection<U> = (U extends any ? (arg: U) => void : never) extends ((arg: infer I) => void) ? I : never | |
type Values<T> = T[keyof T]; |
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