Re: [Boost-users] reference to '_1' is ambiguous

Eric Niebler:

Peter Dimov wrote:

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Eric Niebler: ...

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namespace { // This reference should also be statically initialized placeholder > const & _1 = placeholder_instance >::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.

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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. :-)