Tagged bindings

We can use tagged bindings to fix AMBIGUOUS_MATCH errors when two or more concretions have been bound to an abstraction. Notice how the constructor arguments of the Ninja class have been annotated using the @tagged decorator:

interface Weapon {}

@injectable()
class Katana implements Weapon {}

@injectable()
class Shuriken implements Weapon {}

interface Ninja {
    katana: Weapon;
    shuriken: Weapon;
}

@injectable()
class Ninja implements Ninja {
    public katana: Weapon;
    public shuriken: Weapon;
    public constructor(
        @inject("Weapon") @tagged("canThrow", false) katana: Weapon,
        @inject("Weapon") @tagged("canThrow", true) shuriken: Weapon
    ) {
        this.katana = katana;
        this.shuriken = shuriken;
    }
}

We are binding Katana and Shuriken to Weapon but a whenTargetTagged constraint is added to avoid AMBIGUOUS_MATCH errors:

container.bind<Ninja>(ninjaId).to(Ninja);
container.bind<Weapon>(weaponId).to(Katana).whenTargetTagged("canThrow", false);
container.bind<Weapon>(weaponId).to(Shuriken).whenTargetTagged("canThrow", true);