function createInjector(modulesToLoad) {
  var INSTANTIATING = {},
      providerSuffix = 'Provider',
      path = [],
      loadedModules = new HashMap(),
      providerCache = {
        $provide: {
            provider: supportObject(provider),
            factory: supportObject(factory),
            service: supportObject(service),
            value: supportObject(value),
            constant: supportObject(constant),
            decorator: decorator
          }
      },
      providerInjector = createInternalInjector(providerCache, function() {
        throw Error("Unknown provider: " + path.join(' <- '));
      }),
      instanceCache = {},
      instanceInjector = (instanceCache.$injector =
          createInternalInjector(instanceCache, function(servicename) {
            var provider = providerInjector.get(servicename + providerSuffix);
            return instanceInjector.invoke(provider.$get, provider);
          }));


  forEach(loadModules(modulesToLoad), function(fn) { instanceInjector.invoke(fn || noop); });

  return instanceInjector;

  ////////////////////////////////////
  // $provider
  ////////////////////////////////////

  function supportObject(delegate) {
    return function(key, value) {
      if (isObject(key)) {
        forEach(key, reverseParams(delegate));
      } else {
        return delegate(key, value);
      }
    }
  }

  function provider(name, provider_) {
    if (isFunction(provider_)) {
      provider_ = providerInjector.instantiate(provider_);
    }
    if (!provider_.$get) {
      throw Error('Provider ' + name + ' must define $get factory method.');
    }
    return providerCache[name + providerSuffix] = provider_;
  }

  function factory(name, factoryFn) { return provider(name, { $get: factoryFn }); }

  function service(name, constructor) {
    return factory(name, ['$injector', function($injector) {
      return $injector.instantiate(constructor);
    }]);
  }

  function value(name, value) { return factory(name, valueFn(value)); }

  function constant(name, value) {
    providerCache[name] = value;
    instanceCache[name] = value;
  }

  function decorator(serviceName, decorFn) {
    var origProvider = providerInjector.get(serviceName + providerSuffix),
        orig$get = origProvider.$get;

    origProvider.$get = function() {
      var origInstance = instanceInjector.invoke(orig$get, origProvider);
      return instanceInjector.invoke(decorFn, null, {$delegate: origInstance});
    };
  }

  ////////////////////////////////////
  // Module Loading
  ////////////////////////////////////
  function loadModules(modulesToLoad){
    var runBlocks = [];
    forEach(modulesToLoad, function(module) {
      if (loadedModules.get(module)) return;
      loadedModules.put(module, true);
      if (isString(module)) {
        var moduleFn = angularModule(module);
        runBlocks = runBlocks.concat(loadModules(moduleFn.requires)).concat(moduleFn._runBlocks);

        try {
          for(var invokeQueue = moduleFn._invokeQueue, i = 0, ii = invokeQueue.length; i < ii; i++) {
            var invokeArgs = invokeQueue[i],
                provider = invokeArgs[0] == '$injector'
                    ? providerInjector
                    : providerInjector.get(invokeArgs[0]);

            provider[invokeArgs[1]].apply(provider, invokeArgs[2]);
          }
        } catch (e) {
          if (e.message) e.message += ' from ' + module;
          throw e;
        }
      } else if (isFunction(module)) {
        try {
          runBlocks.push(providerInjector.invoke(module));
        } catch (e) {
          if (e.message) e.message += ' from ' + module;
          throw e;
        }
      } else if (isArray(module)) {
        try {
          runBlocks.push(providerInjector.invoke(module));
        } catch (e) {
          if (e.message) e.message += ' from ' + String(module[module.length - 1]);
          throw e;
        }
      } else {
        assertArgFn(module, 'module');
      }
    });
    return runBlocks;
  }

  ////////////////////////////////////
  // internal Injector
  ////////////////////////////////////

  function createInternalInjector(cache, factory) {

    function getService(serviceName) {
      if (typeof serviceName !== 'string') {
        throw Error('Service name expected');
      }
      if (cache.hasOwnProperty(serviceName)) {
        if (cache[serviceName] === INSTANTIATING) {
          throw Error('Circular dependency: ' + path.join(' <- '));
        }
        return cache[serviceName];
      } else {
        try {
          path.unshift(serviceName);
          cache[serviceName] = INSTANTIATING;
          return cache[serviceName] = factory(serviceName);
        } finally {
          path.shift();
        }
      }
    }

    function invoke(fn, self, locals){
      var args = [],
          $inject,
          length,
          key;

      if (typeof fn == 'function') {
        $inject = inferInjectionArgs(fn);
        length = $inject.length;
      } else {
        if (isArray(fn)) {
          $inject = fn;
          length = $inject.length - 1;
          fn = $inject[length];
        }
        assertArgFn(fn, 'fn');
      }

      for(var i = 0; i < length; i++) {
        key = $inject[i];
        args.push(
          locals && locals.hasOwnProperty(key)
          ? locals[key]
          : getService(key, path)
        );
      }

      // Performance optimization: http://jsperf.com/apply-vs-call-vs-invoke
      switch (self ? -1 : args.length) {
        case  0: return fn();
        case  1: return fn(args[0]);
        case  2: return fn(args[0], args[1]);
        case  3: return fn(args[0], args[1], args[2]);
        case  4: return fn(args[0], args[1], args[2], args[3]);
        case  5: return fn(args[0], args[1], args[2], args[3], args[4]);
        case  6: return fn(args[0], args[1], args[2], args[3], args[4], args[5]);
        case  7: return fn(args[0], args[1], args[2], args[3], args[4], args[5], args[6]);
        case  8: return fn(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7]);
        case  9: return fn(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8]);
        case 10: return fn(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9]);
        default: return fn.apply(self, args);
      }
    }

    function instantiate(Type, locals) {
      var Constructor = function() {},
          instance, returnedValue;

      Constructor.prototype = (isArray(Type) ? Type[Type.length - 1] : Type).prototype;
      instance = new Constructor();
      returnedValue = invoke(Type, instance, locals);

      return isObject(returnedValue) ? returnedValue : instance;
    }

    return {
      invoke: invoke,
      instantiate: instantiate,
      get: getService
    };
  }
}
@ngdoc method
@name angular.module.AUTO.$provide#decorator
@methodOf angular.module.AUTO.$provide
@description

Decoration of service, allows the decorator to intercept the service instance creation. The
returned instance may be the original instance, or a new instance which delegates to the
original instance.

@param {string} name The name of the service to decorate.
@param {function()} decorator This function will be invoked when the service needs to be
   instanciated. The function is called using the {@link angular.module.AUTO.$injector#invoke
   injector.invoke} method and is therefore fully injectable. Local injection arguments:

   * `$delegate` - The original service instance, which can be monkey patched, configured,
     decorated or delegated to.