When compiling managed code in VC++ .NET, which is any of the /clr compiler options, the programmer can mix both CLR classes and regular C++ classes. In the regular C++ classes, Boost should work fine. The VC++ macro which tells one that managed code of any kind is being compiled is _MANAGED, which is defined if managed code is being compiled else it is not defined. So when any of the /clr compiler options are being used _MANAGED is defined, else it is not defined. The VC++ compiler issues compiler warning C4561 whenever managed code is being compiled and __fastcall shows up as a calling convention in any way. Obviously the programmer can turn off this warning via a VC++ #pragma, but I am wondering if Boost could not change some of its headers to avoid this warning. In Boost bind and mem_fn, the programmer has to specifically ask for __fastcall support via special Boost macros to have any functions declared with the __fastcall calling convention, so nothing should be done there since it is clearly a programming error if he does so while compiling managed code. However there are two other places in Boost which I have discovered where functions with the __fastcall calling convention are declared without the programmer doing anything. The first, and most cumbersome reagrding warning messages, is in type_traits in the helper header files type_traits\detail\is_mem_fun_pointer_tester.hpp and type_traits\detail\is_function_pointer_tester.hpp. Since many other libraries, lambda in my case recently, uses type_traits, might not these headers be changed so that when VC++ is the compiler and _MANAGED is defined, the __fastcall versions of these helper functions are not declared ? The second, which I have not encountered but which I saw while searching through Boost header code, is in regex\config.h and I do not know, given some other macros there, whether BOOST_REGEX_CALL can ever be __fastcall when compiling with /clr, but if it can perhaps a change can be made there also. I know that it is not the purpose of Boost to try to accomodate C++ .NET programmers creating /clr compilations using Boost, especially when just warnings and not errors are issued. But in this case, using the predefined macro _MANAGED in VC++ and BOOST_MSVC, it would seem this acoomodation could be made. So I would like the Boost developers of type_traits, especially since it is used by so many other Boost libraries, and regex to consider it.