diff --git a/modules/angular2/src/di/annotations_impl.ts b/modules/angular2/src/di/annotations_impl.ts
index 566e94a27f..42ce53ff05 100644
--- a/modules/angular2/src/di/annotations_impl.ts
+++ b/modules/angular2/src/di/annotations_impl.ts
@@ -15,7 +15,7 @@ import {CONST, stringify} from "angular2/src/facade/lang";
 @CONST()
 export class Inject {
   constructor(public token) {}
-  toString() { return `@Inject(${stringify(this.token)})`; }
+  toString(): string { return `@Inject(${stringify(this.token)})`; }
 }
 
 /**
@@ -34,7 +34,7 @@ export class Inject {
 @CONST()
 export class InjectPromise {
   constructor(public token) {}
-  toString() { return `@InjectPromise(${stringify(this.token)})`; }
+  toString(): string { return `@InjectPromise(${stringify(this.token)})`; }
 }
 
 /**
@@ -53,7 +53,7 @@ export class InjectPromise {
 @CONST()
 export class InjectLazy {
   constructor(public token) {}
-  toString() { return `@InjectLazy(${stringify(this.token)})`; }
+  toString(): string { return `@InjectLazy(${stringify(this.token)})`; }
 }
 
 /**
@@ -72,7 +72,7 @@ export class InjectLazy {
  */
 @CONST()
 export class Optional {
-  toString() { return `@Optional()`; }
+  toString(): string { return `@Optional()`; }
 }
 
 /**
diff --git a/modules/angular2/src/di/binding.ts b/modules/angular2/src/di/binding.ts
index dd9a2e5fd0..705e164d41 100644
--- a/modules/angular2/src/di/binding.ts
+++ b/modules/angular2/src/di/binding.ts
@@ -3,6 +3,7 @@ import {
   isBlank,
   isPresent,
   CONST,
+  CONST_EXPR,
   BaseException,
   stringify,
   isArray
@@ -30,7 +31,7 @@ export class Dependency {
   static fromKey(key: Key) { return new Dependency(key, false, false, false, []); }
 }
 
-var _EMPTY_LIST = [];  // TODO: make const when supported
+const _EMPTY_LIST = CONST_EXPR([]);
 
 /**
  * Describes how the {@link Injector} should instantiate a given token.
diff --git a/modules/angular2/src/di/exceptions.ts b/modules/angular2/src/di/exceptions.ts
index 5b2098eb3e..28e701451b 100644
--- a/modules/angular2/src/di/exceptions.ts
+++ b/modules/angular2/src/di/exceptions.ts
@@ -140,6 +140,7 @@ export class CyclicDependencyError extends AbstractBindingError {
 export class InstantiationError extends AbstractBindingError {
   cause;
   causeKey;
+
   // TODO(tbosch): Can't do key:Key as this results in a circular dependency!
   constructor(cause, key) {
     super(key, function(keys: List<any>) {
diff --git a/modules/angular2/src/di/forward_ref.ts b/modules/angular2/src/di/forward_ref.ts
index a80d4c1652..c3083f1b2d 100644
--- a/modules/angular2/src/di/forward_ref.ts
+++ b/modules/angular2/src/di/forward_ref.ts
@@ -1,4 +1,4 @@
-import {Type, stringify} from 'angular2/src/facade/lang';
+import {Type, stringify, isFunction} from 'angular2/src/facade/lang';
 
 export interface ForwardRefFn { (): any; }
 
@@ -42,7 +42,7 @@ export function forwardRef(forwardRefFn: ForwardRefFn): Type {
  * @exportedAs angular2/di
  */
 export function resolveForwardRef(type: any): any {
-  if (typeof type == 'function' && type.hasOwnProperty('__forward_ref__') &&
+  if (isFunction(type) && type.hasOwnProperty('__forward_ref__') &&
       type.__forward_ref__ === forwardRef) {
     return (<ForwardRefFn>type)();
   } else {
diff --git a/modules/angular2/src/di/key.ts b/modules/angular2/src/di/key.ts
index c1cd355eba..6b2627d09f 100644
--- a/modules/angular2/src/di/key.ts
+++ b/modules/angular2/src/di/key.ts
@@ -5,8 +5,6 @@ import {resolveForwardRef} from './forward_ref';
 
 export {TypeLiteral} from './type_literal';
 
-// TODO: uncoment `int` once https://github.com/angular/angular/issues/1414 is fixed
-
 /**
  * A unique object used for retrieving items from the {@link Injector}.
  *
@@ -20,21 +18,16 @@ export {TypeLiteral} from './type_literal';
  * @exportedAs angular2/di
  */
 export class Key {
-  token: Object;
-  id: number;
-
   /**
    * @private
    */
-  constructor(token: Object, id: number) {
+  constructor(public token: Object, public id: number) {
     if (isBlank(token)) {
       throw new BaseException('Token must be defined!');
     }
-    this.token = token;
-    this.id = id;
   }
 
-  get displayName() { return stringify(this.token); }
+  get displayName(): string { return stringify(this.token); }
 
   /**
    * Retrieves a `Key` for a token.
@@ -51,8 +44,7 @@ export class Key {
  * @private
  */
 export class KeyRegistry {
-  _allKeys: Map<Object, Key>;
-  constructor() { this._allKeys = MapWrapper.create(); }
+  private _allKeys: Map<Object, Key> = MapWrapper.create();
 
   get(token: Object): Key {
     if (token instanceof Key) return token;
@@ -73,7 +65,7 @@ export class KeyRegistry {
     return newKey;
   }
 
-  get numberOfKeys() /* :int */ { return MapWrapper.size(this._allKeys); }
+  get numberOfKeys(): number { return MapWrapper.size(this._allKeys); }
 }
 
 var _globalKeyRegistry = new KeyRegistry();