[Bug c++/57433] New: Local classes have an associated namespace

[potswa at mac dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57433

            Bug ID: 57433
           Summary: Local classes have an associated namespace
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: potswa at mac dot com

The example below should fail with access to a deleted function, but is
accepted by GCC 4.9. Clang correctly rejects it.

The issue is that [basic.lookup.argdep] §3.4.2/2 is defined in terms of
namespace membership, but a local class (such as a lambda) is not a member of a
namespace.

"If T is a class type (including unions), its associated classes are: the class
itself; the class of which it is a member, if any; and its direct and indirect
base classes. Its associated namespaces are the namespaces of which its
associated classes are members."


template< typename t, typename u >
void f( t, u ) = delete;

template< typename t >
void c( t o ) { f( o, 5 ); }

namespace n {
template< typename t >
void f( t, int ) {}

void p() { c( []{} ); }
}


For the sake of argument, the same Standardese forbids the following example
because n2 is only associated with n1, not s. None of its associated classes
are members of a namespace so it is not associated. Such behavior is
ridiculous. GCC and Clang accept this… it would be surprising if any
implementation didn't.

namespace n {
struct s { struct n1 { struct n2 {}; }; };
int f( s::n1::n2 ) { return 3; }
}
int i = f( n::s::n1::n2() );