/**
 * Creates a token that can be used in a DI Provider.
 *
 * Use an `InjectionToken` whenever the type you are injecting is not reified (does not have a
 * runtime representation) such as when injecting an interface, callable type, array or
 * parametrized type.
 *
 * `InjectionToken` is parameterized on `T` which is the type of object which will be returned by
 * the `Injector`. This provides additional level of type safety.
 *
```
interface MyInterface {...}
let myInterface = injector.get(new InjectionToken<MyInterface>('SomeToken'));
// myInterface is inferred to be MyInterface.
```
 *
 * ### Example
 *
```ts
const BASE_URL = new InjectionToken<string>('BaseUrl');
const injector =
    Injector.resolveAndCreate([{token: BASE_URL, useValue: 'http://localhost'}]);
const url = injector.get(BASE_URL);
// here `url` is inferred to be `string` because `BASE_URL` is `InjectionToken<string>`.
expect(url).toBe('http://localhost');
```
 */
export class InjectionToken<T = any> {
  constructor(protected desc: string) {}

  toString(): string {
    return this.desc;
  }
}