[MSVC 10 & 9 & 8] forward declarations of concept checked function templates don't work (compiler bug?)

[Stefan van Kessel <van_kessel@…>]

As posted by Lorenzo Caminiti to comp.lib.boost.devel (8/9/2010) forward declarations of concept checked function templates lead to ambiguity errors even though the function signatures are identical when compiled with MSVC (I tested MSVC 10 & MSVC9, Caminit MSVC8)

I believe it boils down to a compiler error where MSVC fails to recognize that signatures are identical when the return type depends on fairly complex expressions that include non type template arguments. I've got a patch that seems to work for MSVC10. Since I used decltype it doesn't help for the older versions though. I haven't tested it much and I'm sure I'm breaking all kinds of boost coding guidelines but maybe it's of help anyway.

[Stefan van Kessel <van_kessel@…>]

patch for boost\concept\requires.hpp

[Stefan van Kessel <van_kessel@…>]

example code that breaks

[Stefan van Kessel <van_kessel@…>]

Removed unncessary decltype. Now works at least on msvc10 and msvc9

[Stefan van Kessel <van_kessel@…>]

removed unneccsary macros, added value enum member to template to make sure value of _requires_ gets evaluated in absence of decltype(...::value), changed PP condition to use BOOST_TESTED_AT