Как мне вызвать ::std::make_shared в классе только с защищенными или частными конструкторами? ⇐ C++

[Гость]

У меня есть код, который не работает, но думаю, цель ясна:

testmakeshared.cpp

Код: Выделить всё

#include 

class A {
public:
static ::std::shared_ptr create() {
return ::std::make_shared();
}

protected:
A() {}
A(const A &) = delete;
const A &operator =(const A &) = delete;
};

::std::shared_ptr foo()
{
return A::create();
}

Но при компиляции я получаю эту ошибку:

Код: Выделить всё

g++ -std=c++0x -march=native -mtune=native -O3 -Wall testmakeshared.cpp
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr.h:52:0,
from /usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/memory:86,
from testmakeshared.cpp:1:
testmakeshared.cpp: In constructor ‘std::_Sp_counted_ptr_inplace::_Sp_counted_ptr_inplace(_Alloc) [with _Tp = A, _Alloc = std::allocator, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’:
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr_base.h:518:8:   instantiated from ‘std::__shared_count::__shared_count(std::_Sp_make_shared_tag, _Tp*, const _Alloc&, _Args&& ...) [with _Tp = A, _Alloc = std::allocator, _Args = {}, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr_base.h:986:35:   instantiated from ‘std::__shared_ptr::__shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator, _Args = {}, _Tp = A, __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr.h:313:64:   instantiated from ‘std::shared_ptr::shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...) [with _Alloc = std::allocator, _Args = {}, _Tp = A]’
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr.h:531:39:   instantiated from ‘std::shared_ptr std::allocate_shared(const _Alloc&, _Args&& ...) [with _Tp = A, _Alloc = std::allocator, _Args = {}]’
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr.h:547:42:   instantiated from ‘std::shared_ptr std::make_shared(_Args&& ...) [with _Tp = A, _Args = {}]’
testmakeshared.cpp:6:40:   instantiated from here
testmakeshared.cpp:10:8: error: ‘A::A()’ is protected
/usr/lib/gcc/x86_64-redhat-linux/4.6.1/../../../../include/c++/4.6.1/bits/shared_ptr_base.h:400:2: error: within this context

Compilation exited abnormally with code 1 at Tue Nov 15 07:32:58

This message is basically saying that some random method way down in the template instantiation stack from ::std::make_shared can't access the constructor because it's protected.

But I really want to use both ::std::make_shared and prevent anybody from making an object of this class that isn't pointed at by a ::std::shared_ptr. Is there any way to accomplish this?


Источник: https://stackoverflow.com/questions/814 ... vate-const