Extract function parameters or change function return type in mapped types

Search Terms

extract function parameters
change function return type

Suggestion

Allow mapped types to change the return type of a function

Use Cases

I am writing a mocking framework. My system under test might be like this:

MyClass{
    myClassFunction(paramOne: string, paramTwo: number): string{}
}

but in my mocking framework I want to do this:

mockedObject
    .withFunction("myClassFunction")
    .withParameters("paramOneValue", 123)
   .wasCalled();

to do the withParameters I need to type a function with the same parameters as defined on my class but with a different return type.

Checklist

My suggestion meets these guidelines:
[ ] This wouldn't be a breaking change in existing TypeScript / JavaScript code
[ ] This wouldn't change the runtime behavior of existing JavaScript code
[ ] This could be implemented without emitting different JS based on the types of the expressions
[ ] This isn't a runtime feature (e.g. new expression-level syntax)

まず、mocking-framework の例を使って、mapped type と function type に関する TypeScript の機能を調べます。既存の TypeScript と JavaScript の動作を維持しながら、パラメーターの抽出と戻り値の型の置き換えをどのように表現すべきかを判断します。要求された型変換がサポートされ、例にあるモック関数のパラメーターが正しくチェックされれば完了です。