[Bug libstdc++/55977] New: [C++11] vector range construction imposes unnecessary conversion constraints

[Bug libstdc++/55977] New: [C++11] vector range construction imposes unnecessary conversion constraints

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

             Bug #: 55977
           Summary: [C++11] vector 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 compiled with gcc 4.8.0 20130113 (experimental) using the
flags

-Wall -std=c++11 -pedantic

is rejected:

//-------------------------------------
#include <memory>
#include <utility>
#include <vector>
#include <iterator>
#include <iostream>

template <class T>
struct MyAllocator {
  std::allocator<T> base;
  typedef T value_type;
  MyAllocator() = default;
  template <class U>
  MyAllocator(const MyAllocator<U>& other) : base(other.base) {}
  T* allocate(std::size_t n) { return base.allocate(n); }
  void deallocate(T* p, std::size_t n) { return base.deallocate(p, n); }
  template <class U, class... Args>
  void construct(U* p, Args&&... args)
  {
     ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...);
  }
};

struct A {
private:
  friend class MyAllocator<A>;
  A(int value) : value(value) {}
  int value;
public:
  A() : value() {}
  int get() const { return value; }
};

int main()
{
  std::vector<A, MyAllocator<A>> v1;
  const int i = 1;
  v1.emplace_back(i); // OK
  std::vector<A, MyAllocator<A>> v2(std::istream_iterator<int>(std::cin), {});
// Error
}
//-------------------------------------

"[..]gcc\include\c++\4.8.0\bits\stl_vector.h||In instantiation of 'void
std::vector<_Tp, _Alloc>::_M_range_initialize(_InputIterator, _InputIterator,
std::input_iterator_tag) [with _InputIterator = std::istream_iterator<int>; _Tp
= A; _Alloc = MyAllocator<A>]':|
[..]gcc\include\c++\4.8.0\bits\stl_vector.h|1178|required from 'void
std::vector<_Tp, _Alloc>::_M_initialize_dispatch(_InputIterator,
_InputIterator, std::__false_type) [with _InputIterator =
std::istream_iterator<int>; _Tp = A; _Alloc = MyAllocator<A>]'|
[..]gcc\include\c++\4.8.0\bits\stl_vector.h|396|required from 'std::vector<_Tp,
_Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) [with
_InputIterator = std::istream_iterator<int>; <template-parameter-2-2> = void;
_Tp = A; _Alloc = MyAllocator<A>; std::vector<_Tp, _Alloc>::allocator_type =
MyAllocator<A>]'|
main.cpp|38|required from here|
main.cpp|26|error: 'A::A(int)' is private|
[..]gcc\include\c++\4.8.0\bits\stl_vector.h|1188|error: within this context"

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.

The same problem also occurs for other standard containers such as std::list.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-01-14
     Ever Confirmed|0                           |1

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-14 22:18:08 UTC ---
I just notice that the implementation of construct should be changed to

  template <class U, class... Args>
  void construct(U* p, Args&&... args)
  {
     ::new (static_cast<void*>(p)) U(std::forward<Args>(args)...);
  }

instead. The slight difference (Replace T by U) doesn't matter in this example,
but for correctness reasons should be applied.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.8.1

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-03-17 11:22:08 UTC ---
Likewise, thanks Daniel.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

--- Comment #3 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2013-03-18 10:16:07 UTC ---
Author: paolo
Date: Mon Mar 18 10:15:56 2013
New Revision: 196774

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196774
Log:
2013-03-18  Paolo Carlini  <paolo.carlini@oracle.com>

    PR libstdc++/55977 (partial, std::vector and std::deque bits)
    * include/bits/stl_vector.h (_M_range_initialize(_InputIterator,
    _InputIterator, std::input_iterator_tag)): Use emplace_back.
    * include/bits/deque.tcc (_M_range_initialize(_InputIterator,
    _InputIterator, std::input_iterator_tag)): Likewise.
    * testsuite/23_containers/vector/cons/55977.cc: New.
    * testsuite/23_containers/deque/cons/55977.cc: Likewise.
    * testsuite/23_containers/vector/requirements/dr438/assign_neg.cc:
    Adjust dg-error line number.
    * testsuite/23_containers/vector/requirements/dr438/insert_neg.cc:
    Likewise.

Added:
    trunk/libstdc++-v3/testsuite/23_containers/deque/cons/55977.cc
    trunk/libstdc++-v3/testsuite/23_containers/vector/cons/55977.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/deque.tcc
    trunk/libstdc++-v3/include/bits/stl_vector.h
   
trunk/libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/assign_neg.cc
   
trunk/libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/insert_neg.cc

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-03-27 14:33:25 UTC ---
std::vector and std::deque fixed for 4.8.1 too.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.1                       |4.8.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.1 has been released.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.2                       |4.8.3

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.2 has been released.

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.3                       |---

[Bug libstdc++/55977] [C++11] vector range construction imposes unnecessary conversion constraints

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55977

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.8.1
      Known to fail|                            |4.8.0

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This was fixed for 4.8.1