[Bug c++/38502] New: static_assert vs. enums

[bkoz at gcc dot gnu dot org]

C++0x static asserts cannot be used like so:

#include <cassert>

  /// Enumeration for memory_order
  typedef enum memory_order 
    {
      memory_order_relaxed, 
      memory_order_consume, 
      memory_order_acquire, 
      memory_order_release,
      memory_order_acq_rel, 
      memory_order_seq_cst
    } memory_order;

class a
{
  void
  store1(void* __v, memory_order __m = memory_order_seq_cst) volatile
  {
    assert(__m == memory_order_acquire);
    assert(__m == memory_order_acq_rel);
    assert(__m == memory_order_consume);
  }

  void
  store2(void* __v, const memory_order __m = memory_order_seq_cst)
  {
    static_assert(__m == memory_order_acquire, 
                  "atomic_address::store requirements not met.");
    static_assert(__m == memory_order_acq_rel, 
                  "atomic_address::store requirements not met.");
    static_assert(__m == memory_order_consume, 
                  "atomic_address::store requirements not met.");      
  }
};

g++ -std=gnu++0x says:

<bkoz@francisco> /home/bkoz                                                    
%$bld/H-x86-gcc.20081208/bin/g++ -std=gnu++0x -g teststatic_a.cc
teststatic_a.cc: In member function 'void a::store2(void*, memory_order)':
teststatic_a.cc:27: error: '__m' cannot appear in a constant-expression
teststatic_a.cc:29: error: '__m' cannot appear in a constant-expression
teststatic_a.cc:31: error: '__m' cannot appear in a constant-expression


There is an interesting comment in the originating boost static assert header, 
see 'It's not particularly clear how this applies to enum's or typedefs;'
http://www.boost.org/doc/libs/1_37_0/boost/static_assert.hpp

Now for the legalese:

In N2798, 
7.1p4:
  In a static_assert-declaration the constant-expression shall be a constant
expression (5.19) that can be contextually converted to bool (Clause 4).

5.18p3
  A constant expression is an integral constant expression if it is of integral
or enumeration type

>From this, I expect the above code to be valid and compile w/o error.


-- 
           Summary: static_assert vs. enums
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bkoz at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38502