[Bug libstdc++/55979] New: [C++11] std::list range construction imposes unnecessary conversion constraints

["daniel.kruegler at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55979

             Bug #: 55979
           Summary: [C++11] std::list range construction imposes
                    unnecessary conversion constraints
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


The following code provided by Jonathan compiled with gcc 4.8.0 20130113
(experimental) using the flags

-Wall -std=c++11 -pedantic

is rejected:

//-------------------------------
#include <list>

struct A
{
  A(int) { }
  A(const A&) = delete;
  A& operator=(const A&) = delete;
};

int main()
{
  int i[] = {1, 2};
  std::list<A> li(i, i + 2);
}
//-------------------------------

"[..]gcc\include\c++\4.8.0\bits\stl_list.h||In instantiation of
'std::_List_node<_Tp>::_List_node(_Args&& ...) [with _Args = {A}; _Tp = A]':|
[..]\gcc\include\c++\4.8.0\ext\new_allocator.h|120|required from 'void
__gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up =
std::_List_node<A>; _Args = {A}; _Tp = std::_List_node<A>]'|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|506|required from 'std::list<_Tp,
_Alloc>::_Node* std::list<_Tp, _Alloc>::_M_create_node(_Args&& ...) [with _Args
= {A}; _Tp = A; _Alloc = std::allocator<A>; std::list<_Tp, _Alloc>::_Node =
std::_List_node<A>]'|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|1558|required from 'void
std::list<_Tp, _Alloc>::_M_insert(std::list<_Tp, _Alloc>::iterator, _Args&&
...) [with _Args = {A}; _Tp = A; _Alloc = std::allocator<A>; std::list<_Tp,
_Alloc>::iterator = std::_List_iterator<A>]'|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|1022|required from 'void
std::list<_Tp, _Alloc>::push_back(std::list<_Tp, _Alloc>::value_type&&) [with
_Tp = A; _Alloc = std::allocator<A>; std::list<_Tp, _Alloc>::value_type = A]'|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|1491|required from 'void
std::list<_Tp, _Alloc>::_M_initialize_dispatch(_InputIterator, _InputIterator,
std::__false_type) [with _InputIterator = int*; _Tp = A; _Alloc =
std::allocator<A>]'|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|628|required from 'std::list<_Tp,
_Alloc>::list(_InputIterator, _InputIterator, const allocator_type&) [with
_InputIterator = int*; <template-parameter-2-2> = void; _Tp = A; _Alloc =
std::allocator<A>; std::list<_Tp, _Alloc>::allocator_type =
std::allocator<A>]'|
main.cpp|13|required from here|
[..]gcc\include\c++\4.8.0\bits\stl_list.h|115|error: use of deleted function
'A::A(const A&)'|
main.cpp|6|error: declared here
"

The error is due to a call of push_back with an previous int->A conversion. 

Such an conversion from the iterator's value_type to the containers value_type
is not feasible. The specification of the corresponding constructor is
(indirectly) ruled by Table 100, expression X(i, j):

"Requires: T shall be EmplaceConstructible into X from *i."

Move/CopyConstructible or Convertible to value_type are not required.

Instead of invoking push_back this constructor should internally invoke the
equivalent of emplace_back.

This issue is similar to bug 55977 involving std::vector, but occurs even with
the default allocator and for all iterator categories except input iterator,
therefore this issue is reported separately.