可变模板:整数参数到lambda的完美转发

也有类似的问题,但我没有找到一个适合我的问题的答案。

考虑以下代码:

#include <cassert>
#include <functional>
#include <iostream>
#include <memory>
#include <utility>

class TestClass
{
public:
   TestClass( int value): mValue( value) { }
private:
   int  mValue;
};

template< typename T> class DeferredCreator
{
public:
   template< class... Args> DeferredCreator( Args&&... args):
      mpCreator( [=]() -> T*
         { return new T( std::forward< Args>( args)...);  }
      ),
      mpObject()
   { }

   T* get() {
      if (mpObject == nullptr)
         mpObject.reset( mpCreator());
      return mpObject.get();
   }
private:
   std::function< T*( void)>  mpCreator;
   std::unique_ptr< T>        mpObject;
};


int main() {
   DeferredCreator< int>  dcInt( 42);

   assert( dcInt.get() != nullptr);
   return 0;
}

prog.cpp:19:26: error: no matching function for call to 'forward'
         { return new T( std::forward< Args>( args)...);  }
                         ^~~~~~~~~~~~~~~~~~~
prog.cpp:36:27: note: in instantiation of function template specialization 'DeferredCreator<int>::DeferredCreator<int>' requested here
   DeferredCreator< int>  dcInt( 42);
                          ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/move.h:76:5: note: candidate function not viable: 1st argument ('const int') would lose const qualifier
    forward(typename std::remove_reference<_Tp>::type& __t) noexcept
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/bits/move.h:87:5: note: candidate function not viable: 1st argument ('const int') would lose const qualifier
    forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
    ^
2 errors generated.

decltype( args) 作为的模板参数 std::forward<> ,但这没有帮助。

代码也可在此处获得: https://ideone.com/MIhMkt