Typescript：如何在函数中使用泛型类型

Question

I have the following structure:

export interface Complex {
    getId<T>(entity: T): string
}

const test: Complex = {
    getId<Number>(entity){return "1"} // does not work 'entity is implicitly any'
}

Why do I have to declare the type of entity as entity:Number in order to make it work?

Answer 1

Because you declare interface which has a Generic Type Function ( getById ).

To reference to generic as a type, you must do this:

interface Complex<T> {
  getId(entity: T): string;
}

const test: Complex<Number> = {
  getId(entity) {
    return entity.toString();
  }
}

The use-case of what you did might be following:

interface AbstractFactory {
  create<T>(data: T): string;
}

const factory: AbstractFactory = {
  create<T>(data: T): string {
    return data.toString();
  }
}

factory.create<Number>(123);