Pass bound values as const values to the bound function

base/bind.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_BIND_H_
 #define BASE_BIND_H_
 
 #include "base/bind_internal.h"
 
 // -----------------------------------------------------------------------------
@@ skipping 52 matching lines @@
 template <typename Functor, typename... Args>
 using MakeUnboundRunType =
     typename internal::MakeUnboundRunTypeImpl<Functor, Args...>::Type;
 
 template <typename Functor, typename... Args>
 base::Callback<MakeUnboundRunType<Functor, Args...>>
 Bind(Functor functor, Args&&... args) {
   // Type aliases for how to store and run the functor.
   using RunnableType = typename internal::FunctorTraits<Functor>::RunnableType;
   using RunType = typename internal::FunctorTraits<Functor>::RunType;
-
-  // Use RunnableType::RunType instead of RunType above because our
-  // checks below for bound references need to know what the actual
-  // functor is going to interpret the argument as.
-  using BoundRunType = typename RunnableType::RunType;
-
-  using BoundArgs =
-      internal::TakeTypeListItem<sizeof...(Args),
-                                 internal::ExtractArgs<BoundRunType>>;
-
-  // Do not allow binding a non-const reference parameter. Non-const reference
-  // parameters are disallowed by the Google style guide.  Also, binding a
-  // non-const reference parameter can make for subtle bugs because the
-  // invoked function will receive a reference to the stored copy of the
-  // argument and not the original.
-  static_assert(!internal::HasNonConstReferenceItem<BoundArgs>::value,
-                "do not bind functions with nonconst ref");
-
   const bool is_method = internal::HasIsMethodTag<RunnableType>::value;
 
   // For methods, we need to be careful for parameter 1.  We do not require
   // a scoped_refptr because BindState<> itself takes care of AddRef() for
   // methods. We also disallow binding of an array as the method's target
   // object.
   static_assert(!internal::BindsArrayToFirstArg<is_method, Args...>::value,
                 "first bound argument to method cannot be array");
   static_assert(
       !internal::HasRefCountedParamAsRawPtr<is_method, Args...>::value,
       "a parameter is a refcounted type and needs scoped_refptr");
 
   using BindState = internal::BindState<RunnableType, RunType, Args...>;
 
   return Callback<typename BindState::UnboundRunType>(
       new BindState(internal::MakeRunnable(functor),
                     std::forward<Args>(args)...));
 }
 
 }  // namespace base
 
 #endif  // BASE_BIND_H_