Re: [boost] Visual Studio 2015 Update 3 hasremovedstd::unary_functionand std::binary_function

but I have a hunch that all Apple versions will behave in this way. Not sure about libc++ on other platforms such as Linux.

Yeah, we don't have a tester using libc++ on Linux, but its source is here: http://llvm.org/svn/llvm-project/libcxx/trunk/include/__locale and there's no primary definition. So it's not version specific and not Apple specific.