[Bug c++/52174] New: Implicit conversion of nullptr to bool

[Bug c++/52174] New: Implicit conversion of nullptr to bool

[lsoltysiak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

             Bug #: 52174
           Summary: Implicit conversion of nullptr to bool
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: trivial
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: lsoltysiak@gmail.com


Document 'A name for the null pointer: nullptr (revision 4)' states that
implicit conversion of nullptr to bool is not allowed. Unfortunately in g++
4.7.0, this requirement is not fulfilled. See example below.


if (nullptr) //shall return error, implicit conversion to bool not allowed

[Bug c++/52174] Implicit conversion of nullptr to bool

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-08 16:53:43 UTC ---
That document is not the standard, [conv.bool] says "A prvalue of type
std::nullptr_t can be converted to a prvalue of type bool; the resulting value
is false."

[Bug c++/52174] Implicit conversion of nullptr to bool

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-08 16:55:26 UTC ---
but N.B. http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1423

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |SUSPENDED
   Last reconfirmed|                            |2012-02-08
         Resolution|INVALID                     |
            Summary|Implicit conversion of      |[DR 1423] Implicit
                   |nullptr to bool             |conversion of nullptr to
                   |                            |bool
     Ever Confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-08 18:05:19 UTC ---
that DR has been discussed by the committee today and it seems the rule will be
changed, so suspending

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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> 2012-07-20 18:58:28 UTC ---
DR 1423 has now reached ready status, 

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1423

so this seems like a good reason to consider a compiler change to evaluate
potential code breakages.

Here some recommended test-cases that should hold:

1)

bool b1 = nullptr; // Is well-formed today, needs to be ill-formed

2)

bool b2(nullptr); // well-formed today and under 1423

3)

template<class T>
T&& make();

template<class T>
void sink(T);

template<class T1, class T2,
  class = decltype(sink<T2>(make<T1>()))
>
auto f(int) -> char(&)[1];

template<class, class>
auto f(...) -> char(&)[2];

static_assert(sizeof(f<decltype(nullptr), bool>(0)) != 1, "");

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|SUSPENDED                   |NEW
           Severity|trivial                     |normal

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-10-05 19:31:08 UTC ---
Unsuspending then.

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
   Target Milestone|---                         |4.10.0

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Mine.

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

--- Comment #7 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Tue Jun  3 17:48:36 2014
New Revision: 211195

URL: http://gcc.gnu.org/viewcvs?rev=211195&root=gcc&view=rev
Log:
gcc/cp
2014-06-03  Paolo Carlini  <paolo.carlini@oracle.com>

    DR 1423
    PR c++/52174
    * call.c (standard_conversion): Convert nullptr to bool only
    in case of direct-initialization.
    (convert_like_real): Provide informative error message.

gcc/testsuite
2014-06-03  Paolo Carlini  <paolo.carlini@oracle.com>

    DR 1423
    PR c++/52174
    * g++.dg/cpp0x/nullptr31.C: New.
    * g++.dg/cpp0x/sfinae-nullptr1.C: Likewise.
    * g++.dg/cpp0x/nullptr17.C: Update.

libstdc++-v3
2014-06-03  Paolo Carlini  <paolo.carlini@oracle.com>

    DR 1423
    PR c++/52174
    * testsuite/20_util/is_assignable/value.cc: Update.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/nullptr31.C
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae-nullptr1.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/nullptr17.C
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/testsuite/20_util/is_assignable/value.cc

[Bug c++/52174] [DR 1423] Implicit conversion of nullptr to bool

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52174

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 4.10.0.