Reference class type parameters in static members #32246
Description
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.