ReplaceKeys

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题目

Implement a type ReplaceKeys, that replace keys in union types, if some type has not this key, just skip replacing, A type takes three arguments.

For example:

type NodeA = {
  type: "A";
  name: string;
  flag: number;
};

type NodeB = {
  type: "B";
  id: number;
  flag: number;
};

type NodeC = {
  type: "C";
  name: string;
  flag: number;
};

type Nodes = NodeA | NodeB | NodeC;

type ReplacedNodes = ReplaceKeys<
  Nodes,
  "name" | "flag",
  { name: number; flag: string }
>; // {type: 'A', name: number, flag: string} | {type: 'B', id: number, flag: string} | {type: 'C', name: number, flag: string} // would replace name from string to number, replace flag from number to string.

type ReplacedNotExistKeys = ReplaceKeys<Nodes, "name", { aa: number }>; // {type: 'A', name: never, flag: number} | NodeB | {type: 'C', name: never, flag: number} // would replace name to never

解答

type ReplaceKeys<U, T, Y> = {
  [K in keyof U]: K extends T ? (K extends keyof Y ? Y[K] : never) : U[K];
};