Reference class type parameters in static members

[ardalanamini]

Search Terms

static, generic, type, class, model, inheritance

Suggestion

Static class members should be allowed to reference the class's type parameters.

Use Cases

A very simple use case is in database models such as the example given below.
At the moment there's no way provided by the TypeScript to deal with such a problem which is the main reason we use this language, type safety!

Examples

Expected behavior:

class Model<T extends object = any> {
  public static all(): Promise<T[]> {
    // code
  }

  public static first(): Promise<T> {
    // code
  }
}

class User extends Model<{ username: string }> {}

User.all(); // Promise<Array<{ username: string }>>
User.first(); // Promise<{ username: string }>

The behavior we got to deal with: (which can add more typing error easily)

class Model {
  public static all<T extends object = any>(): Promise<T[]> {
    // code
  }

  public static first<T extends object = any>(): Promise<T> {
    // code
  }
}

class User extends Model {}

User.all<{ username: string }>(); // Promise<Array<{ username: string }>>
User.first<{ username: string }>(); // Promise<{ username: string }>

This bahavior is unacceptable since it needs the developer to reference the item interface every time he/she calls these sort of methods, which doesn't seem to satisfy the soul purpose of the TypeScript

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, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[RyanCavanaugh]

Duplicate
#32211
#24018
and probably others

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.