Add the inject() function (#60)

Author: vbraun

lib/index.ts

@@ -25,3 +25,4 @@ export { InjectionToken, OpaqueToken } from './injection_token';
 export { Class, TypeDecorator, makeDecorator, makeParamDecorator, makePropDecorator } from './util/decorators';
 export { resolveDependencies } from './util/resolve_dependencies';
 export { Type, isType } from './facade/type';
+export { inject } from './injector_compatibility';

lib/injector_compatibility.ts

@@ -0,0 +1,36 @@
+import { Type } from "./facade/type";
+import { InjectionToken } from "./injection_token";
+import { Injector } from "./injector";
+
+
+/**
+ * Current injector value used by `inject`.
+ * - `undefined`: it is an error to call `inject`
+ * - Injector instance: Use the injector for resolution.
+ */
+let _currentInjector: Injector | undefined = undefined;
+
+export function getCurrentInjector(): Injector | undefined {
+  return _currentInjector;
+}
+
+
+export function setCurrentInjector(
+  injector: Injector | undefined,
+): Injector | undefined {
+  const former = _currentInjector;
+  _currentInjector = injector;
+  return former;
+}
+
+
+export function inject<T>(token: Type<T> | InjectionToken<T>): T {
+  if (_currentInjector === undefined) {
+    throw new Error(
+      `inject() must be called from an injection context such as a constructor, a factory function, or a field initializer`,
+    );
+  } else {
+    const value = _currentInjector.get(token);
+    return value;
+  }
+}

lib/reflective_injector.ts

@@ -6,7 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import { Type } from './facade/type';
 import { Injector, THROW_IF_NOT_FOUND } from './injector';
+import { setCurrentInjector } from './injector_compatibility';
 import { Self, SkipSelf } from './metadata';
 import { Provider } from './provider';
 import { cyclicDependencyError, instantiationError, noProviderError, outOfBoundsError } from './reflective_errors';
@@ -333,7 +335,7 @@ export class ReflectiveInjector_ implements ReflectiveInjector {
   }
 
   instantiateResolved(provider: ResolvedReflectiveProvider): any {
-    return this._instantiateProvider(provider);
+    return this._instantiateProviderContext(provider);
   }
 
   getProviderAtIndex(index: number): ResolvedReflectiveProvider {
@@ -348,13 +350,22 @@ export class ReflectiveInjector_ implements ReflectiveInjector {
     if (this._constructionCounter++ > this._getMaxNumberOfObjects()) {
       throw cyclicDependencyError(this, provider.key);
     }
-    return this._instantiateProvider(provider);
+    return this._instantiateProviderContext(provider);
   }
 
   private _getMaxNumberOfObjects(): number {
     return this.objs.length;
   }
 
+  private _instantiateProviderContext(provider: ResolvedReflectiveProvider): any {
+    const previousInjector = setCurrentInjector(this);
+    try {
+      return this._instantiateProvider(provider);
+    } finally {
+      setCurrentInjector(previousInjector);
+    }
+  }
+
   private _instantiateProvider(provider: ResolvedReflectiveProvider): any {
     if (provider.multiProvider) {
       const res = new Array(provider.resolvedFactories.length);

test/reflective_injector_spec.ts

@@ -19,6 +19,7 @@ import {
   ReflectiveKey,
   Self,
   forwardRef,
+  inject,
 } from '../lib';
 import { ReflectiveInjector_ } from '../lib/reflective_injector';
 import { ResolvedReflectiveProvider_ } from '../lib/reflective_provider';
@@ -41,6 +42,13 @@ class Dashboard {
   constructor(software: DashboardSoftware) {}
 }
 
+class GloveboxManual {}
+
+@Injectable()
+class Glovebox {
+  manual = inject(GloveboxManual);
+}
+
 class TurboEngine extends Engine {}
 
 @Injectable()
@@ -351,6 +359,13 @@ describe(`injector`, () => {
     const injector = createInjector([{ provide: 'null', useValue: null }]);
     expect(injector.get('null')).toBe(null);
   });
+
+  it('should support the inject() function', () => {
+    const injector = createInjector([Glovebox, GloveboxManual]);
+    const glovebox = injector.get(Glovebox);
+    expect(glovebox instanceof Glovebox).toBe(true);
+    expect(glovebox.manual instanceof GloveboxManual).toBe(true);
+  });
 });
 
 describe('child', () => {