是否有可能（还）返回一个输入对象，其输入类型按属性映射？

Question

In short, I want a function which takes an non-predefined type like this:

{
  name: string,
  list: Array,
  metadata: Object,
}

and returns this

{
  name: MyStringProxy,
  list: MyArrayProxy,
  metadata: MyObjectProxy,
}

---

I know how to get an object returned where every property has the same type ( Object with the same keys as another object in typescript? )...

abstract function allPropsAre42<TYPE_IN>(obj: TYPE_IN): { [key in keyof TYPE_IN]: 42 };

...which is a good starting point, but it only maps everything to one type. I want to map each type to another.

---

I'm pretty sure it isn't possible, but here's some made up pseudo-code which would be like what I'm looking for:

interface IPropMap {
  string: MyStringProxy,
  Array: MyListProxy,
  Object: MyObjectProxy,
}
// not real code
abstract function mapAllProps<TYPE_IN>(obj: TYPE_IN): { 
 [key in keyof TYPE_IN]: IPropMap[TYPE_IN[key]]
};

Is it possible to do such a thing in typescript?

Answer 1

https://www.typescriptlang.org/docs/handbook/advanced-types.html#conditional-types

Figured it out. Using conditional type mapping, this can be done:

type TypeName<T> =
    T extends string ? MyStringProxy :
    T extends Array ? MyArrayProxy :
    T extends object ? MyObjectProxy :
    undefined;


abstract function mapAllProps<TYPE_IN>(obj: TYPE_IN): { 
 [key in keyof TYPE_IN]: TypeName[TYPE_IN[key]]
};

My guess wasn't too far off.