Callback support for unbound reference and array arguments.

base/callback.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
 $$
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 $$
 
 $var MAX_ARITY = 6
 
 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
@@ skipping 222 matching lines @@
 
 $if ARITY == 0 [[
 template <typename R>
 class Callback<R(void)> : public internal::CallbackBase {
 ]] $else [[
 template <typename R, $for ARG , [[typename A$(ARG)]]>
 class Callback<R($for ARG , [[A$(ARG)]])> : public internal::CallbackBase {
 ]]
 
  public:
-  typedef R(*PolymorphicInvoke)(internal::InvokerStorageBase*[[]]
+  typedef R(*PolymorphicInvoke)(
+      internal::InvokerStorageBase*[[]]
 $if ARITY != 0 [[, ]]
-$for ARG ,
-                                [[const A$(ARG)&]]);
+$for ARG , [[typename internal::ParamTraits<A$(ARG)>::ForwardType]]);
 
   Callback() : CallbackBase(NULL, NULL) { }
 
   // We pass InvokerStorageHolder by const ref to avoid incurring an
   // unnecessary AddRef/Unref pair even though we will modify the object.
   // We cannot use a normal reference because the compiler will warn
   // since this is often used on a return value, which is a temporary.
   //
   // Note that this constructor CANNOT be explicit, and that Bind() CANNOT
   // return the exact Callback<> type.  See base/bind.h for details.
   template <typename T>
   Callback(const internal::InvokerStorageHolder<T>& invoker_holder)
       : CallbackBase(
           reinterpret_cast<InvokeFuncStorage>(&T::Invoker::DoInvoke),
           &invoker_holder.invoker_storage_) {
   }
 
   R Run($for ARG ,
-        [[const A$(ARG)& a$(ARG)]]) const {
+        [[typename internal::ParamTraits<A$(ARG)>::ForwardType a$(ARG)]]) const {
     PolymorphicInvoke f =
         reinterpret_cast<PolymorphicInvoke>(polymorphic_invoke_);
 
     return f(invoker_storage_.get()[[]]
 $if ARITY != 0 [[, ]]
 $for ARG ,
              [[a$(ARG)]]);
   }
 };
 
 
 ]]  $$ for ARITY
 
 // Syntactic sugar to make Callbacks<void(void)> easier to declare since it
 // will be used in a lot of APIs with delayed execution.
 typedef Callback<void(void)> Closure;
 
 }  // namespace base
 
 #endif  // BASE_CALLBACK_H