Restricting or Fixing the Generic Type Parameter

Classes podem prover uma implementação de uma interface que é especifica para um tipo ou subconjunto de tipos suportados pela interface:

import {City, Person, Product, Employee} from "./dataTypes";

type  shapeType = { name: string };

interface Collection<T extends shapeType> {
    add(...newItems: T[]): void;

    get(name: string): T;

    count: number;
}

class PersonCollection implements Collection<Person> {
    private items: Person[] = [];

    add(...newItems: Person[]): void {
        this.items.push(...newItems);
    }

    get(name: string): Person {
        return this.items.find(item => item.name === name);
    }

    get count(): number {
        return this.items.length;
    }
}

let peopleCollection: Collection<Person> = new PersonCollection();
peopleCollection.add(new Person("Bob Smith", "London"),
    new Person("Dora Peters", "New York"));
console.log(`Collection size: ${peopleCollection.count}`);

05 December 2025