[Bug c++/64665] New: Overload resolution not working with std::initializer_list<std::string> and bool

[Bug c++/64665] New: Overload resolution not working with std::initializer_list<std::string> and bool

[duncan.forster at mac dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

            Bug ID: 64665
           Summary: Overload resolution not working with
                    std::initializer_list<std::string> and bool
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: duncan.forster at mac dot com

Created attachment 34482
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34482&action=edit
gcc -v

Test case.

#include <string>
#include <iostream>

void Test1(const bool arg) 
{
    std::cout << "Right[" << arg << "] (standard conversion sequence)" <<
std::endl;
}
void Test1(const std::string arg)
{
    std::cout << "Wrong[" << arg.size() << "] (user-defined conversion
sequence)" << std::endl;
}

void Test2(const int arg) 
{
    std::cout << "Wrong[" << arg << "] (no conversion, doesn't initializes
std::initializer_list)" << std::endl;
}
void Test2(const std::initializer_list<int> arg)
{
    std::cout << "Right[" << arg.size() << "] (no conversion, initializes
std::initializer_list)" << std::endl;
}

struct S 
{ 
    S(int _a) : a(_a){}
    int getA() const { return a; }
private:
    int a;
};
void Test3(const int arg) 
{
    std::cout << "Right[" << arg << "] (standard conversion sequence)" <<
std::endl;
}
void Test3(const S arg)
{
    std::cout << "Wrong[" << arg.getA() << "] (user-defined conversion
sequence)" << std::endl;
}

void Test4(const bool arg) 
{
    std::cout << "Right[" << arg << "] (standard conversion sequence)" <<
std::endl;
}
void Test4(const std::initializer_list<std::string> arg)
{
    std::cout << "Wrong[" << arg.size() << "] (user-defined conversion
sequence)" << std::endl;
}

int main (int /*argc*/, char * const /*argv*/[]) 
{
    Test1({"false"});
    Test2({123});
    Test3({456});
    Test4({"false"});
    return 0;
}

GCC should print:
  Right[1] (standard conversion sequence)
  Right[1] (no conversion, initializes std::initializer_list)
  Right[456] (standard conversion sequence)
  Right[1] (standard conversion sequence)

GCC prints this instead:
  Right[1] (standard conversion sequence)
  Right[1] (no conversion, initializes std::initializer_list)
  Right[456] (standard conversion sequence)
  Wrong[1] (user-defined conversion sequence)

Here are the two conversion sequences for Test4:

  {const char[6]} -> {const char*} -> {bool} (standard conversion sequence)
  {const char[6]} -> {const char*} -> {std::string::ctor} (user-defined
conversion sequence)

The standard conversion sequence should be preferred over a user-defined
conversion sequence.

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-19
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Possibly a duplicate of another bug but I can't find one right now.

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

Richard Smith <richard-gccbugzilla at metafoo dot co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |richard-gccbugzilla@metafoo
                   |                            |.co.uk

--- Comment #2 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> ---
Per DR1467, a list-initialization sequence that initializes
std::initializer_list is always better than one that does not; I think this is
invalid.

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[duncan.forster at mac dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

--- Comment #3 from Duncan Forster <duncan.forster at mac dot com> ---
(In reply to Richard Smith from comment #2)
I've been back and forth about what is correct behavior , in the end I think
you're correct. GCC seems to be doing the right thing according to the latest
C++ defect reports.

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Shouldn't we add the testcase to gcc testsuite nevertheless, or do we have this
covered in the testsuite already?

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Let's add a reduced testcase and close the bug.

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

--- Comment #6 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Thu Mar  5 09:15:58 2015
New Revision: 221207

URL: https://gcc.gnu.org/viewcvs?rev=221207&root=gcc&view=rev
Log:
2015-03-05  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/64665
    * g++.dg/cpp0x/initlist92.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/initlist92.C
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug c++/64665] Overload resolution not working with std::initializer_list<std::string> and bool

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64665

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

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

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done.