Eric Niebler:
Peter Dimov wrote:
Eric Niebler: ...
namespace { // This reference should also be statically initialized placeholder<mpl::int_<1> > const & _1 = placeholder_instance<mpl::int_<1> >::value; }
This is a problem for some precompiled header implementations.
Huh.
Yep. Apparently, the unnamed namespace does not get an unique name in every translation unit because of the precompilation.
Some compilers have fixed theirs to allow it, some have not, some only allow(ed?) it when the variables are static.
I notice I left "static" out of the example I sent around, but yes, placeholder_instance<>::value is supposed to be a class static.
This is not what I meant. On some compilers (going by the #ifdefs, MSVC and Metrowerks), this: namespace { X x; } doesn't work in a precompiled header, but this: namespace { static X x; } does (because a static x doesn't cause a multiple definition link error.) On Borland, neither works in a PCH. On g++ 4, both work but the second causes an "unused variable" warning for every _K that is not referenced, which is a bit annoying. I'm not sure what works on g++ 3, but it uses the inline function path. :-)