[Bug c++/60511] New: [C++1y][N3652] Missing extended constexpr function support

[Bug c++/60511] New: [C++1y][N3652] Missing extended constexpr function support

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60511

            Bug ID: 60511
           Summary: [C++1y][N3652] Missing extended constexpr function
                    support
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daniel.kruegler at googlemail dot com

gcc 4.9.0 20140309 (experimental) compiled with the flags

-std=c++1y -Wall -pedantic

rejects:

//----------------------
template<class T>
struct L 
{
  T t;
  constexpr L(const T& t) : t(t) {}
  constexpr const T& value() const & { return t; }
  constexpr T& value() & { return t; }
};

template<class T>
constexpr T twice(const T& t) {
  L<T> l(t);
  l.value() *= 2;
  return l.value();
}

int main() {
  constexpr int i = twice(12);
  static_assert(i == 24, "");
}
//----------------------

<quote>
prog.cc:7:16: error: 'constexpr T& L<T>::value() const &' cannot be overloaded 
   constexpr T& value() & { return t; } 
               ^ 
prog.cc:6:22: error: with 'constexpr const T& L<T>::value() const &' 
   constexpr const T& value() const & { return t; } ^ 

prog.cc: In instantiation of 'constexpr T twice(const T&) [with T = int]': 
prog.cc:18:29: required from here 
prog.cc:13:13: error: assignment of read-only location 'l.L<T>::value<int>()' 
   l.value() *= 2; 
             ^ 
prog.cc:15:1: error: body of constexpr function 'constexpr T twice(const T&)
[with T = 
int]' not a return-statement 
 } 
 ^ 
prog.cc: In function 'int main()': 
prog.cc:18:29: error: 'constexpr T twice(const T&) [with T = int]' called in a 
constant expression 
   constexpr int i = twice(12); 
                              ^ 
prog.cc:11:13: note: 'constexpr T twice(const T&) [with T = int]' is not usable
as 
a constexpr function because: 
 constexpr T twice(const T& t) { 
             ^
</quote>

The compiler seems currently not apply the extended C++14 constexpr rules as of

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3652.html

1) constexpr makes non-static member functions automatically const member
functions

2) constexpr functions require a single return statement

3) constexpr functions reject mutable operations

[Bug c++/60511] [C++1y][N3652] Missing extended constexpr function support

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60511

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at redhat dot com,
                   |                            |ville.voutilainen at gmail dot com
      Known to work|                            |5.0

--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
The current trunk accepts the testcase (and implements C++14 relaxed
constexpr). Shouldn't this be closed?

[Bug c++/60511] [C++1y][N3652] Missing extended constexpr function support

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60511

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |FIXED
   Target Milestone|---                         |5.0

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Implemented for GCC 5.