Шаблонный ход ctor для обёрнутого unique_ptr

Я хочу, чтобы что-то вроде unique_ptr, но гарантированно (в пределах разумного) было ненулевым. Я написал этот класс, который содержит unique_ptr, и я написал этот конструктор перемещения, который, как я надеялся, позволил бы мне создавать и перемещать один из моих указателей из другого, при условии, что базовый unique_ptr может быть сконструирован аналогичным образом. Итак, сначала я попробую что-нибудь простое; создать указатель на int из указателя на int.

#include <memory>
#include <utility>
#include <cassert>template<
typename T
>
class Nonup
{
private:

std::unique_ptr<T> m_ptr;

public:

explicit Nonup( T* p )
: m_ptr( p )
{ assert( p ); }

Nonup( const Nonup& ) = delete;
Nonup& operator=( const Nonup& ) = delete;

template<typename U>
Nonup( Nonup<U>&& old )
:
m_ptr( std::move( old ) )
{}

Nonup& operator=( Nonup&& rhs ) = default;

decltype( *m_ptr ) operator*() const { return *m_ptr; }
};int main()
{
Nonup<int> first( new int( 42 ) );

Nonup<int> second( std::move( first ) );

return 0;
}

Почему g ++ 4.7.0 дает ошибки при перемещении-построении переменной second? Вывод «g ++ -std = c ++ 11 main.cpp» выглядит следующим образом.

main.cpp: In instantiation of ‘Nonup<T>::Nonup(Nonup<U>&&) [with U = int; T = int]’:
main.cpp:40:43:   required from here
main.cpp:27:37: error: no matching function for call to ‘std::unique_ptr<int, std::default_delete<int> >::unique_ptr(std::remove_reference<Nonup<int>&>::type)’
main.cpp:27:37: note: candidates are:
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/memory:86:0,
from main.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:164:2: note: template<class _Up, class> std::unique_ptr::unique_ptr(std::auto_ptr<_Up>&&)
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:164:2: note:   template argument deduction/substitution failed:
main.cpp:27:37: note:   ‘std::remove_reference<Nonup<int>&>::type {aka Nonup<int>}’ is not derived from ‘std::auto_ptr<_Up>’
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/memory:86:0,
from main.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:155:2: note: template<class _Up, class _Ep, class> std::unique_ptr::unique_ptr(std::unique_ptr<_Up, _Ep>&&)
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:155:2: note:   template argument deduction/substitution failed:
main.cpp:27:37: note:   ‘std::remove_reference<Nonup<int>&>::type {aka Nonup<int>}’ is not derived from ‘std::unique_ptr<_Up, _Ep>’
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/memory:86:0,
from main.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:142:7: note: std::unique_ptr<_Tp, _Dp>::unique_ptr(std::unique_ptr<_Tp, _Dp>&&) [with _Tp = int; _Dp = std::default_delete<int>]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:142:7: note:   no known conversion for argument 1 from ‘std::remove_reference<Nonup<int>&>::type {aka Nonup<int>}’ to ‘std::unique_ptr<int, std::default_delete<int> >&&’
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:136:17: note: constexpr std::unique_ptr<_Tp, _Dp>::unique_ptr(std::nullptr_t) [with _Tp = int; _Dp = std::default_delete<int>; std::nullptr_t = std::nullptr_t]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:136:17: note:   no known conversion for argument 1 from ‘std::remove_reference<Nonup<int>&>::type {aka Nonup<int>}’ to ‘std::nullptr_t’
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:130:7: note: std::unique_ptr<_Tp, _Dp>::unique_ptr(std::unique_ptr<_Tp, _Dp>::pointer, typename std::remove_reference<_To>::type&&) [with _Tp = int; _Dp = std::default_delete<int>; std::unique_ptr<_Tp, _Dp>::pointer = int*; typename std::remove_reference<_To>::type = std::default_delete<int>]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:130:7: note:   candidate expects 2 arguments, 1 provided
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:125:7: note: std::unique_ptr<_Tp, _Dp>::unique_ptr(std::unique_ptr<_Tp, _Dp>::pointer, typename std::conditional<std::is_reference<_Dp>::value, _Dp, const _Dp&>::type) [with _Tp = int; _Dp = std::default_delete<int>; std::unique_ptr<_Tp, _Dp>::pointer = int*; typename std::conditional<std::is_reference<_Dp>::value, _Dp, const _Dp&>::type = const std::default_delete<int>&]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:125:7: note:   candidate expects 2 arguments, 1 provided
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:120:7: note: std::unique_ptr<_Tp, _Dp>::unique_ptr(std::unique_ptr<_Tp, _Dp>::pointer) [with _Tp = int; _Dp = std::default_delete<int>; std::unique_ptr<_Tp, _Dp>::pointer = int*]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:120:7: note:   no known conversion for argument 1 from ‘std::remove_reference<Nonup<int>&>::type {aka Nonup<int>}’ to ‘std::unique_ptr<int, std::default_delete<int> >::pointer {aka int*}’
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:114:17: note: constexpr std::unique_ptr<_Tp, _Dp>::unique_ptr() [with _Tp = int; _Dp = std::default_delete<int>]
/usr/lib/gcc/x86_64-redhat-linux/4.7.0/../../../../include/c++/4.7.0/bits/unique_ptr.h:114:17: note:   candidate expects 0 arguments, 1 provided

Спасибо!