Any ideas on this one? From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Jonathan Leonard Sent: Thursday, April 02, 2009 2:13 PM To: boost-users@lists.boost.org Subject: [Boost-users] [mpl] newbie question about if_c et al Hi, I'm trying to make a class which is conditionally synchronized. What I have is like the following: template<bool SYNCH=true> class c { public: void f() { typename boost::mpl::if_c<SYNCH, ScopedCriticalSection<>, void*>::type scs(cs); // SCS == RAII wrapper around CS // do other stuff } private: typename boost::mpl::if_c<SYNCH, CriticalSection<>, void*>::type cs; }; This is not entirely optimal though as it requires 3 MOV instructions to create the scs void* copy when SYNCH is false (and I'd rather not lean on compiler optimizations even if they will help in this case). [Something like NullType, VoidType, or OptionType (a la F#) would be ideal but I can't seem to locate one (and I'm not sure the type system would allow such a thing-it doesn't seem to like a simple 'void']. Any better idiom or alternative approach anyone can offer for this purpose would be greatly appreciated. Many thanks, Jonathan