[Bug c++/56319] New: call to implicitly-deleted copy constructor accepted

[Bug c++/56319] New: call to implicitly-deleted copy constructor accepted

[wlodzimierz.lipert at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

             Bug #: 56319
           Summary: call to implicitly-deleted copy constructor accepted
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: wlodzimierz.lipert@gmail.com


Hi,

GCC compiles following code. Copying of tuple of rvalues returned by:
std::forward_as_tuple, should not be allowed because it is ill formed.
(clang++ properly detects the problem and report an error.)
/*----------------------------------------------------------------------------*/
template <unsigned int ...>
struct TupleIndices
{};

template<
        unsigned int I,
        typename IndexTuple,
        typename... Types>
struct MakeTupleIndices_;

template<
         unsigned int I,
         unsigned int... Indices,
         typename T,
         typename... Types>
struct MakeTupleIndices_<I, TupleIndices<Indices...>, T, Types...>
{
    typedef typename MakeTupleIndices_<I + 1, TupleIndices<Indices..., I>,
Types...>::type type;
};

template<
        unsigned int I,
        unsigned int... Indices>
        struct MakeTupleIndices_<I, TupleIndices<Indices...> >
{
    typedef TupleIndices<Indices...> type;
};

template<typename... Types>
struct MakeTupleIndices : public MakeTupleIndices_<0, TupleIndices<>, Types...>
{};
/*----------------------------------------------------------------------------*/
void bar(int)
{
}

template <typename... Args, unsigned int... ArgsIndices>
void fooImpl(std::tuple<Args...> args, TupleIndices<ArgsIndices...>)
{
        bar(std::forward<Args>(std::get<ArgsIndices>(args))...);
}

template <typename... Args>
void foo(std::tuple<Args...> args)
{
    fooImpl(args, typename MakeTupleIndices<Args...>::type());
}
/*----------------------------------------------------------------------------*/
enum
{
    id = 1
};

int main()
{
    foo(std::forward_as_tuple(id));
    return 0;
}
/*----------------------------------------------------------------------------*/

Wlodzimierz.

[Bug c++/56319] implicit copy constructor is not deleted when it is ill formed

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |normal

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-14 12:32:31 UTC ---
reduced:

#include <tuple>

template <typename... Args>
void fooImpl(std::tuple<Args...> args)
{
}

template <typename... Args>
void foo(std::tuple<Args...> args)
{
    fooImpl(args);
}

enum E { id };

int main()
{
    foo(std::forward_as_tuple(id));
    return 0;
}

[Bug c++/56319] implicit copy constructor is not deleted when it is ill formed

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-14 12:36:56 UTC ---
Reduced to remove <tuple> dependency

template<typename T>
struct tuple
{
    T t;
};

template<class... Types>
tuple<Types&&...> forward_as_tuple(Types&&... t) noexcept
{
    return tuple<Types&&...>{ static_cast<Types&&>(t)... };
}

template <typename... Args>
void fooImpl(tuple<Args...> args)
{
}

template <typename... Args>
void foo(tuple<Args...> args)
{
    fooImpl(args);
}

enum E { id };

int main()
{
    foo(forward_as_tuple(id));
    return 0;
}

[Bug c++/56319] [DR 1051] implicit copy constructor is not deleted for type with rvalue reference member

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-02-14
            Summary|implicit copy constructor   |[DR 1051] implicit copy
                   |is not deleted when it is   |constructor is not deleted
                   |ill formed                  |for type with rvalue
                   |                            |reference member
     Ever Confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-14 12:45:16 UTC ---
And a minimal form:

struct T { int&& i; };
T t { 1 };
T tt = t;

This should be rejected by [class.copy]/11, this was DR 1051

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1051

[Bug c++/56319] [DR 1051] implicit copy constructor is not deleted for type with rvalue reference member

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #4 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-02-14 20:36:52 UTC ---
Seems to be a dup of bug 55017

[Bug c++/56319] [DR 1051] implicit copy constructor is not deleted for type with rvalue reference member

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56319

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-14 20:47:27 UTC ---
Thanks, Daniel

*** This bug has been marked as a duplicate of bug 55017 ***