anchor.diff:     */
     void type(Type id, {Type implementedBy, CreationStrategy creation,
         Visibility visibility}) {
  -    _providersCache = null;
  +    _dirty();
       _providers[id] = new _TypeProvider(
           implementedBy == null ? id : implementedBy, creation, visibility);
     }
  
positive.code:    */
    void value(Type id, value,
        {CreationStrategy creation, Visibility visibility}) {
      _providersCache = null;
      _providers[id] = new _ValueProvider(value, creation, visibility);
    }
  
  
negative.code:    */
    void install(Module module) {
      _childModules.add(module);
      _dirty();
    }
  
    _dirty() {
      _providersCache = null;
    }
  
    bool get _isDirty =>
        _providersCache == null || _childModules.any((m) => m._isDirty);
  }
  
  /** Deafault creation strategy is to instantiate on the defining injector. */
  