如何在 Typescript 定义中表示对象键替换？

Question

目前我有以下types：

type PossibleKeys = number | string | symbol;
type ValueOf<T extends object> = T[keyof T]; 
type ReplaceKeys<T extends Record<PossibleKeys, any>, U extends Partial<Record<keyof T, PossibleKeys>>> = 
  Omit<T, keyof U> & { [P in ValueOf<U>]: T[keyof U] };

...但是，虽然它甚至可以部分工作，但它给出了以下错误：

类型 'U[keyof U]' 不能分配给类型 'string |号码 | 符号'。

---

A simple demo:

interface Item {
  readonly description: string;
  readonly id: string;
}

interface MyInterface {
  readonly id: string;
  readonly propToReplace: number;
  readonly anotherPropToReplace: readonly Item[];
}

type ReplacedUser = ReplaceKeys<MyInterface, { propToReplace: 'total', anotherPropToReplace: 'items' }>;

在ReplacedUser 我可以看到类型几乎是正确的。推断类型为：

{ id: string; total: number | readonly Item[]; items: number | readonly Item[]; }

...在我期待的时候：

{ id: string; total: number; items: readonly Item[]; }

---

我做错了什么？我首先想知道如何表达P 需要获取U 中传递的值 以抑制Typescript 错误，然后获取特定value 的正确类型。

Answer 1

最简单的方法是为您的ReplaceKeys 反转U 类型参数：

type PossibleKeys = number | string | symbol;
type ReplaceKeys<T extends {}, U extends Record<PossibleKeys, keyof T>> = Omit<T, ValueOf<U>> & {
    [K in keyof U]: T[U[K]]
};

然后你可以像这样使用它：

type ReplacedUser = ReplaceKeys<MyInterface, { total: 'propToReplace', items: 'anotherPropToReplace' }>;

如果你不能改变 U 的形状变得有点棘手：

// Example types from your post
interface Item {
  readonly description: string;
  readonly id: string;
}

interface MyInterface {
  readonly id: string;
  readonly propToReplace: number;
  readonly anotherPropToReplace: readonly Item[];
}

// All possible key types
type PossibleKeys = number | string | symbol;

// Helper type to get all non-nullable values from type T
type DefinedValues<T> = NonNullable<T[keyof T]>;

// Helper type for your replacements object - a record whose values are valid keys
// and whose keys are also present in type T (the input type)
// 
// Partial is used to make sure you don't need to pass all keys of T in your replacements
type Replacements<T extends {}> = Partial<Record<keyof T, PossibleKeys>>;

// Helper type that swaps object keys for values
type Invert<T extends Replacements<C>, C extends {} = {}> = {
  [N in DefinedValues<T>]: {
    [K in keyof T]: N extends T[K] ? K : never
  }[keyof T]
}

type ReplacedKeys<T extends {}, R extends Replacements<T>> = Omit<T, keyof R | DefinedValues<R>> & {
  [N in keyof Invert<R>]: {
    [L in keyof R]: N extends R[L] ? (L extends keyof T ? T[L] : never) : never;
  }[keyof R]
}

请注意，使用第二种方法不会警告您存在重复映射：

type ReplacedUser = ReplacedKeys<MyInterface, { propToReplace: 'total', anotherPropToReplace: 'total' }>;

检查playground here。