[Bug c++/58713] New: error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[Bug c++/58713] New: error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[ali.baharev at gmail dot com]

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[-- Attachment #1: Type: text/plain; charset="UTF-8", Size: 11863 bytes --]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

            Bug ID: 58713
           Summary: error: cannot bind ‘std::ostream {aka
                    std::basic_ostream<char>}’ lvalue to
                    ‘std::basic_ostream<char>&&’
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ali.baharev at gmail dot com

#include <iostream>

struct A { };

int main() {
    A a;
    std::cout << a;
}
-----

g++ 4.8.1, 64 bit with -std=c++11 gives the correct error message:

main.cpp:7:15: error: no match for ‘operator<<’ (operand types are
‘std::ostream {aka std::basic_ostream<char>}’ and ‘A’)
     std::cout << a;
               ^

However, 4.8.1, 32 bit or 4.7.2, 64 bit gives:

prog.cpp:7:18: error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’
lvalue to ‘std::basic_ostream<char>&&’
     std::cout << a;
                  ^
In file included from /usr/include/c++/4.8/iostream:39:0,
                 from prog.cpp:1:
/usr/include/c++/4.8/ostream:602:5: error:   initializing argument 1 of
‘std::basic_ostream<_CharT, _Traits>&
std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT
= char; _Traits = std::char_traits<char>; _Tp = A]’
     operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
     ^

Could this rather confusing error message be improved?

Why do the 32 and 64 bit versions behave differently?
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Subject: [Bug c/58488] -Wuninitialized is useless for a variable whose address is later taken
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58488

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mimomorin at gmail dot com

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
*** Bug 58711 has been marked as a duplicate of this bug. ***
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Subject: [Bug middle-end/58711] Missing "uninitialized" warning in loop condition (when compiling without optimization)
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58711

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

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----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |manu at gcc dot gnu.org
         Resolution|---                         |DUPLICATE

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Known issue.

*** This bug has been marked as a duplicate of bug 58488 ***
>From gcc-bugs-return-431581-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun Oct 13 12:39:29 2013
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From: "ali.baharev at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/58714] New: Bogus value category in ternary operator?
Date: Sun, 13 Oct 2013 12:39:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58714

            Bug ID: 58714
           Summary: Bogus value category in ternary operator?
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ali.baharev at gmail dot com

struct X {
  X& operator=(const X&) = delete;
  X& operator=(X&& ) = default;
};

void f(bool t) {
  X a, b;
  *(t ? &a : &b) = X();
  (t ? a : b) = X();
}
-----
The line:

  (t ? a : b) = X();

gives:

error: use of deleted function ‘X& X::operator=(const X&)’

The code compiles with clang++ 3.4. 

The sections in the Standard relevant here are: [expr.cond]/4 "If the second
and third operands [of the conditional operator] are glvalues of the same value
category and have the same type, the result is of that type and value category"
(text in brackets inserted for clarity).

This code was posted at stackoverflow.com/q/19341908/341970
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Subject: [Bug libgomp/58691] OpenMP 4: Surprising results with OMP_PLACESDate: Sun, 13 Oct 2013 12:41:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX691

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #3)
> That command line doesn't set explicit OMP_PROC_BINDúlse, it sets
> OMP_PLACES twice,

Ups!

> I'll go ahead and commit the patch.

Thanks! Looks good to me. As the issue is solved and as OMP_PLACES is new in
GCC 4.9, I close this bug as FIXED.


> libgomp.texi needs much more updates for OpenMP 4.0

I will create a patch for the run-time library and environment variable parts
of the documentation. But I leave the libgomp API update to you.

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Ali Baharev from comment #0)
> Could this rather confusing error message be improved?

I've tried to improve it in the past, but I think there's no easy way to do it.


> Why do the 32 and 64 bit versions behave differently?

They don't.  I think maybe you forgot to use -std=c++11 in the first case?

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[ali.baharev at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #2 from Ali Baharev <ali.baharev at gmail dot com> ---
>> Why do the 32 and 64 bit versions behave differently?
> 
> They don't.  I think maybe you forgot to use -std=c++11 in the first case?

Yes, that's what happened. Sorry, my mistake.

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #3 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Jonathan Wakely from comment #1)
> I've tried to improve it in the past, but I think there's no easy way to do
> it.

A possible fix might be to change the Standard ;-) Despite the smiley I
seriously consider to make the proposal/open an issue that the "all-eating"
signature

template <class charT, class traits, class T>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>&& os, const T& x);

should be constrained and should not participate in overload resolution unless
the expression

os << x

would be well-formed (similar for the corresponding extractor). My current
guess is that this would also improve the diagnostics in this case, is that
right?
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Subject: [Bug sanitizer/58718] Invalid check in libsanitizer
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX718

Alexey Samsonov <samsonov at google dot com> changed:

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----------------------------------------------------------------------------
                 CC|                            |samsonov at google dot com

--- Comment #2 from Alexey Samsonov <samsonov at google dot com> ---
I've already fixed the problem with crashes caused by small
"malloc_context_size" values. I think you should wait till the ASan runtime
will be merged from LLVM into GCC.

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #4 from Marc Glisse <glisse at gcc dot gnu.org> ---
If I try to sfinae-out this function based on os<<x being well-formed, I get an
error that "template instantiation depth exceeds maximum of 900" (even for a
valid cout<<42), because even if this overload won't match, it still looks at
it recursively.

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #5 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Marc Glisse from comment #4)
> If I try to sfinae-out this function based on os<<x being well-formed, I get
> an error that "template instantiation depth exceeds maximum of 900" (even
> for a valid cout<<42), because even if this overload won't match, it still
> looks at it recursively.

Thanks for your test, Marc. I will reflect upon the problem in a bit more
detail (Let me add that I had thought a while longer about that problem before
this issue cam up but when I added my note to the issue about the actual sfinae
form this was just of the top of my head).
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Subject: [Bug tree-optimization/57511] [4.8 Regression] Missing SCEV final value replacement
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Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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----------------------------------------------------------------------------
                 CC|                            |masoud_mxm at yahoo dot com

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
*** Bug 58717 has been marked as a duplicate of this bug. ***

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #6 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Daniel Krügler from comment #5)
> Thanks for your test, Marc. I will reflect upon the problem in a bit more
> detail

My current guess is that my suggested approach should work, assuming a proper
helper trait template will be used. Here is the model code that I used for
testing:

//---------------------------
#include <type_traits>
#include <utility>

namespace xstd {

template<class CharT = char>
struct OStream 
{
  OStream& operator<<(int);
  OStream& operator<<(short);
  OStream& operator<<(double);
  OStream& operator<<(const void*);
};

struct is_ostreamable_impl 
{
  template<class CharT, class T, class =
    decltype(std::declval<OStream<CharT>&>() << std::declval<T>())>
  static std::true_type test(int);

  template<class, class>
  static std::false_type test(...);
};

template<class CharT, class T>
struct is_ostreamable 
  : decltype(is_ostreamable_impl::test<CharT, T>(0))::type
{  
};

template<class CharT, class T,
  typename std::enable_if<
    is_ostreamable<CharT, const T&>::value, 
    bool
  >::type = false>
  OStream<CharT>& operator<<(OStream<CharT>&& os, const T& t) 
{
  return os << t;
}

OStream<> out;

}

struct A {};

int main() {
  A a;
  xstd::out << 1;
  xstd::out << a;
}
//---------------------------

The diagnostics of my gcc current 4.9.0 is

<quote>
main.cpp||In function 'int main()':|
main.cpp|50|error: no match for 'operator<<' (operand types are
'xstd::OStream<>' and 'A')|
main.cpp|50|note: candidates are:|
main.cpp|9|note: xstd::OStream<CharT>& xstd::OStream<CharT>::operator<<(int)
[with CharT = char]|
main.cpp|9|note:   no known conversion for argument 1 from 'A' to 'int'|
main.cpp|10|note: xstd::OStream<CharT>& xstd::OStream<CharT>::operator<<(short
int) [with CharT = char]|
main.cpp|10|note:   no known conversion for argument 1 from 'A' to 'short int'|
main.cpp|11|note: xstd::OStream<CharT>&
xstd::OStream<CharT>::operator<<(double) [with CharT = char]|
main.cpp|11|note:   no known conversion for argument 1 from 'A' to 'double'|
main.cpp|12|note: xstd::OStream<CharT>& xstd::OStream<CharT>::operator<<(const
void*) [with CharT = char]|
main.cpp|12|note:   no known conversion for argument 1 from 'A' to 'const
void*'|
main.cpp|36|note: template<class CharT, class T, typename
std::enable_if<xstd::is_ostreamable<CharT, const T&>::value, bool>::type
<anonymous> > xstd::OStream<CharT>& xstd::operator<<(xstd::OStream<CharT>&&,
const T&)|
main.cpp|36|note:   template argument deduction/substitution failed:|
main.cpp|35|error: no type named 'type' in 'struct std::enable_if<false,
bool>'|
main.cpp|35|note: invalid template non-type parameter|
</quote>
>From gcc-bugs-return-431655-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Oct 14 13:18:50 2013
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Subject: [Bug libfortran/58015] FAIL: gfortran.dg/round_4.f90: Unsatisfied symbol "nextafterl"
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX015

Rainer Orth <ro at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|hppa64-hp-hpux11.11         |hppa64-hp-hpux11.11,
                   |                            |*-*-solaris2.9
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-10-14
                 CC|                            |ro at gcc dot gnu.org
               Host|hppa64-hp-hpux11.11         |hppa64-hp-hpux11.11,
                   |                            |*-*-solaris2.9
   Target Milestone|---                         |4.9.0
     Ever confirmed|0                           |1
              Build|hppa64-hp-hpux11.11         |hppa64-hp-hpux11.11,
                   |                            |*-*-solaris2.9

--- Comment #5 from Rainer Orth <ro at gcc dot gnu.org> ---
Also on Solaris 9, both SPARC and x86.

  Rainer

[Bug c++/58713] error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}’ lvalue to ‘std::basic_ostream<char>&&’

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58713

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Daniel Krügler from comment #3)
> guess is that this would also improve the diagnostics in this case, is that
> right?

Even if it worked (which it doesn't, as Marc also discovered) it would only
help a little bit, because G++ still prints all the candidates even if they are
not viable due to substitution failure. (Usually I love this feature, but when
there are a very large number of overloads, such as anything using operator<<,
the diagnostics can be overwhelming.)

(In reply to Daniel Krügler from comment #6)
> The diagnostics of my gcc current 4.9.0 is
> 
> <quote>
> main.cpp||In function 'int main()':|
> main.cpp|50|error: no match for 'operator<<' (operand types are
> 'xstd::OStream<>' and 'A')|
> main.cpp|50|note: candidates are:|
> main.cpp|9|note: xstd::OStream<CharT>& xstd::OStream<CharT>::operator<<(int)
> [with CharT = char]|
> main.cpp|9|note:   no known conversion for argument 1 from 'A' to 'int'|
> main.cpp|10|note: xstd::OStream<CharT>&
> xstd::OStream<CharT>::operator<<(short int) [with CharT = char]|
> main.cpp|10|note:   no known conversion for argument 1 from 'A' to 'short
> int'|
> main.cpp|11|note: xstd::OStream<CharT>&
> xstd::OStream<CharT>::operator<<(double) [with CharT = char]|
> main.cpp|11|note:   no known conversion for argument 1 from 'A' to 'double'|
> main.cpp|12|note: xstd::OStream<CharT>&
> xstd::OStream<CharT>::operator<<(const void*) [with CharT = char]|
> main.cpp|12|note:   no known conversion for argument 1 from 'A' to 'const
> void*'|
> main.cpp|36|note: template<class CharT, class T, typename
> std::enable_if<xstd::is_ostreamable<CharT, const T&>::value, bool>::type
> <anonymous> > xstd::OStream<CharT>& xstd::operator<<(xstd::OStream<CharT>&&,
> const T&)|
> main.cpp|36|note:   template argument deduction/substitution failed:|
> main.cpp|35|error: no type named 'type' in 'struct std::enable_if<false,
> bool>'|
> main.cpp|35|note: invalid template non-type parameter|
> </quote>

This does look better.  I thought I'd experimented with a similar trait(*) and
found the results disappointing.

(*)
https://gitorious.org/redistd/redistd/source/33d8d3a4f49da25e71ca87aab674d3b88500d302:include/redi/printers.h
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Subject: [Bug c++/58708] string literal operator templates broken
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX708

--- Comment #5 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
The const qualification of the first parm and the number of elements are wrong.
 I'm testing a patch.