feat(di): introduce aliasing

Closes angular#710 Closes angular#747

Author: pkozlowski-opensource

modules/angular2/docs/di/di.md

@@ -96,7 +96,7 @@ var car = child.get(Car); // uses the Car binding from the parent injector and E
 
 ## Bindings
 
-You can bind to a class, a value, or a factory
+You can bind to a class, a value, or a factory. It is also possible to alias existing bindings.
 
 ```
 var inj = new Injector([
@@ -128,6 +128,16 @@ var inj = new Injector([
 ]);
 ```
 
+If you want to alias an existing binding, you can do so using `toAlias`:
+
+```
+var inj = new Injector([
+bind(Engine).toClass(Engine),
+bind("engine!").toAlias(Engine)
+]);
+```
+which implies `inj.get(Engine) === inj.get("engine!")`.
+
 Note that tokens and factory functions are decoupled.
 
 ```

modules/angular2/src/di/binding.js

@@ -60,6 +60,15 @@ export class BindingBuilder {
  );
  }
 
+ toAlias(aliasToken):Binding {
+ return new Binding(
+ Key.get(this.token),
+ (aliasInstance) => aliasInstance,
+ [new Dependency(Key.get(aliasToken), false, false, [])],
+ false
+ );
+ }
+
  toFactory(factoryFunction:Function, dependencies:List = null):Binding {
  return new Binding(
  Key.get(this.token),

modules/angular2/test/di/injector_spec.js

@@ -128,6 +128,26 @@ export function main() {
  expect(car.engine).toBeAnInstanceOf(Engine);
  });
 
+ it('should bind to an alias', function() {
+ var injector = new Injector([
+ Engine,
+ bind(SportsCar).toClass(SportsCar),
+ bind(Car).toAlias(SportsCar)
+ ]);
+
+ var car = injector.get(Car);
+ var sportsCar = injector.get(SportsCar);
+ expect(car).toBeAnInstanceOf(SportsCar);
+ expect(car).toBe(sportsCar);
+ });
+
+ it('should throw when the aliased binding does not exist', function () {
+ var injector = new Injector([
+ bind('car').toAlias(SportsCar)
+ ]);
+ expect(() => injector.get('car')).toThrowError('No provider for SportsCar! (car -> SportsCar)');
+ });
+
  it('should support overriding factory dependencies', function () {
  var injector = new Injector([
  Engine,
@@ -324,4 +344,4 @@ export function main() {
  });
  });
  });
-}
+}