Typescript类型体操 - MapTypes

题目

中文

实现 MapTypes<T, R>, 它将对象 T 中的类型转换为有如下结构的类型 R 定义的类型

type StringToNumber = {
    mapFrom: string; // 类型为 string 的键(key)
    mapTo: number; // 会被转换为 number
};

示例:

type StringToNumber = { mapFrom: string; mapTo: number };
MapTypes<{ iWillBeANumberOneDay: string }, StringToNumber>; // 结果 { iWillBeANumberOneDay: number; }

注意, 用户可能会传入联合(union)类型

type StringToNumber = { mapFrom: string; mapTo: number };
type StringToDate = { mapFrom: string; mapTo: Date };
MapTypes<{ iWillBeNumberOrDate: string }, StringToDate | StringToNumber>; // gives { iWillBeNumberOrDate: number | Date; }

如果类型在字典中不存在, 那就让它保持原样

type StringToNumber = { mapFrom: string; mapTo: number };
MapTypes<
    { iWillBeANumberOneDay: string; iWillStayTheSame: Function },
    StringToNumber
>; // // gives { iWillBeANumberOneDay: number, iWillStayTheSame: Function }

English

Implement MapTypes<T, R> which will transform types in object T to different types defined by type R which has the following structure

type StringToNumber = {
    mapFrom: string; // value of key which value is string
    mapTo: number; // will be transformed for number
};

Examples:

type StringToNumber = { mapFrom: string; mapTo: number };
MapTypes<{ iWillBeANumberOneDay: string }, StringToNumber>; // gives { iWillBeANumberOneDay: number; }

Be aware that user can provide a union of types:

type StringToNumber = { mapFrom: string; mapTo: number };
type StringToDate = { mapFrom: string; mapTo: Date };
MapTypes<{ iWillBeNumberOrDate: string }, StringToDate | StringToNumber>; // gives { iWillBeNumberOrDate: number | Date; }

If the type doesn't exist in our map, leave it as it was:

type StringToNumber = { mapFrom: string; mapTo: number };
MapTypes<
    { iWillBeANumberOneDay: string; iWillStayTheSame: Function },
    StringToNumber
>; // // gives { iWillBeANumberOneDay: number, iWillStayTheSame: Function }

答案

type MapTypes<T, R extends { mapFrom: unknown; mapTo: unknown }> = {
    [P in keyof T]: T[P] extends R['mapFrom']
        ? R extends R
            ? Equal<T[P], R['mapFrom']> extends true
                ? R['mapTo']
                : never
            : never
        : T[P];
};

在线演示