Generics Aliasing and Partial Specialization

ソースファイル、テスト、エントリーポイントは指定されていません。まず、aliasing と partial specialization の例、および TypeScript の設計目標を確認してください。完了とするには、generic aliases と partial specialization の合意された設計に加えて、要求されたケースの実装とカバレッジが必要です。

Suggestion

🔍 Search Terms

List of keywords you searched for before creating this issue. Write them down here so that others can find this suggestion more easily and help provide feedback.
generics specialization

✅ Viability 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. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Add Generics aliasing and partial Specialization

📃 Aliasing Example

// In external library

export type Monoid<T> = {
  concat: (x: T, y: T) => T;
  empty: T;
};
export type MonoidFn<T> = (concat: (x: T, y: T) => T, empty: T) => Monoid<T>;

// in user code
const monoid: MonoidFn<~T> = (concat, empty) => ({ concat, empty }); // impossible today, T is undefined

Here we want the monoid function to still be generic and still using the original library generic definition. Using ~T tells the compiler we know that T is undefined, just make an alias.

📃 Partial Specialization Example

// In external library

export type AggregateFn<T, U> =  (map: (item: T) => U) => (array: T[]) => U;

// in user code
const sum: AggregateFn<~T, number> = mapReduceSum<T,number>(); // impossible today, T is undefined

Here we want to specialize AggregateFn and make sum an AggregateFn<T, number>, that is still generic but specialized for numbers. Using ~T tells the compiler we know that T is undefined, so make a partial specialization.

💻 Use Cases

This is almost madatory for decent functional programming without having to redeclare functions of an external library.
Examples should be sufficient to explain a basic use case