Adding Angular's DI package & Dart unittests which test it.

third_party/pkg/di/lib/module.dart

+part of di;
+
+typedef dynamic FactoryFn(Injector injector);
+
+/**
+ * Creation strategy is asked to return an instance of the type after
+ * [Injector.get] locates the defining injector that has no instance cached.
+ * [directInstantation] is true when an instance is created directly from
+ * [Injector.instantiate].
+ */
+typedef dynamic CreationStrategy(
+  Injector requesting,
+  Injector defining,
+  dynamic factory()
+);
+
+/**
+ * Visibility determines if the instance in the defining module is visible to
+ * the requesting injector. If true is returned, then the instance from the
+ * defining injector is provided. If false is returned, the injector keeps
+ * walking up the tree to find another visible instance.
+ */
+typedef bool Visibility(Injector requesting, Injector defining);
+
+
+/**
+ * A collection of type bindings. Once the module is passed into the injector,
+ * the injector creates a copy of the module and all subsequent changes to the
+ * module have no effect.
+ */
+class Module {
+  final Map<Type, _Provider> _providers = <Type, _Provider>{};
+  final List<Module> _childModules = <Module>[];
+
+  Map<Type, _Provider> _providersCache;
+
+  /**
+   * Compiles and returs bindings map by performing depth-first traversal of the
+   * child (installed) modules.
+   */
+  Map<Type, _Provider> get _bindings {
+    if (_providersCache == null) {
+      _providersCache = <Type, _Provider>{};
+      _childModules.forEach((child) => _providersCache.addAll(child._bindings));
+      _providersCache.addAll(_providers);
+    }
+    return _providersCache;
+  }
+
+  /**
+   * Register binding to a concrete value.
+   *
+   * The [value] is what actually will be injected.
+   */
+  void value(Type id, value,
+      {CreationStrategy creation, Visibility visibility}) {
+    _providersCache = null;
+    _providers[id] = new _ValueProvider(value, creation, visibility);
+  }
+
+  /**
+   * Register binding to a [Type].
+   *
+   * The [implementedBy] will be instantiated using [new] operator and the
+   * resulting instance will be injected. If no type is provided, then it's
+   * implied that [id] should be instantiated.
+   */
+  void type(Type id, {Type implementedBy, CreationStrategy creation,
+      Visibility visibility}) {
+    _providersCache = null;
+    _providers[id] = new _TypeProvider(
+        implementedBy == null ? id : implementedBy, creation, visibility);
+  }
+
+  /**
+   * Register binding to a factory function.abstract
+   *
+   * The [factoryFn] will be called and all its arguments will get injected.
+   * The result of that function is the value that will be injected.
+   */
+  void factory(Type id, FactoryFn factoryFn,
+      {CreationStrategy creation, Visibility visibility}) {
+    _providersCache = null;
+    _providers[id] = new _FactoryProvider(factoryFn, creation, visibility);
+  }
+
+  /**
+   * Installs another module into this module. Bindings defined on this module
+   * take precidence over the installed module.
+   */
+  void install(Module module) {
+    _childModules.add(module);
+    _providersCache = null;
+  }
+}
+
+/** Deafault creation strategy is to instantiate on the defining injector. */
+dynamic _defaultCreationStrategy(Injector requesting, Injector defining,
+    dynamic factory()) => factory();
+
+/** By default all values are visible to child injectors. */
+bool _defaultVisibility(_, __) => true;
+
+
+typedef Object ObjectFactory(Type type, Injector requestor);
+
+abstract class _Provider {
+  final CreationStrategy creationStrategy;
+  final Visibility visibility;
+
+  _Provider(this.creationStrategy, this.visibility);
+
+  dynamic get(Injector injector, Injector requestor, ObjectFactory getInstanceByType, error);
+}
+
+class _ValueProvider extends _Provider {
+  dynamic value;
+
+  _ValueProvider(this.value, [CreationStrategy creationStrategy,
+                              Visibility visibility])
+      : super(creationStrategy, visibility);
+
+  dynamic get(Injector injector, Injector requestor, ObjectFactory getInstanceByType, error) =>
+      value;
+}
+
+class _TypeProvider extends _Provider {
+  final Type type;
+
+  _TypeProvider(this.type, [CreationStrategy creationStrategy,
+                            Visibility visibility])
+      : super(creationStrategy, visibility);
+
+  dynamic get(Injector injector, Injector requestor, ObjectFactory getInstanceByType, error) =>
+      injector.newInstanceOf(type, getInstanceByType, requestor, error);
+
+}
+
+class _FactoryProvider extends _Provider {
+  final Function factoryFn;
+
+  _FactoryProvider(this.factoryFn, [CreationStrategy creationStrategy,
+                                    Visibility visibility])
+      : super(creationStrategy, visibility);
+
+  dynamic get(Injector injector, Injector requestor, getInstanceByType, error) =>
+      factoryFn(injector);
+}