From: TONGARI J Hi folks,
It's over 2 years since this post: http://boost.2283326.n4.nabble.com/New-powerful-way-to-use-enable-if-in-C-0x...
The macro looks sweet and I wonder if we have this macro in Boost in case that I missed it.
This is nice for C++11 and conversion operators, I was not aware of this trick. However, it would be nice if boost provided requires macros to make it easier to specify traits for enable_if. See here for an implementation: https://github.com/pfultz2/Zen/blob/master/zen/requires.h So functions can be defined like this: template<class T, class U> ZEN_FUNCTION_REQUIRES(is_arithmetic<T>, is_arithmetic<U>) (T) max(T x, U y) { return x > y : x ? y; } All the traits our inclusive by default, but the `exclude` keyword can be used to exclude the trait, like this: template<class T, class U> ZEN_FUNCTION_REQUIRES ( is_arithmetic<T>, is_arithmetic<U>, exclude is_same<T, bool>, exclude is_same<U, bool> ) (T) max(T x, U y) { return x > y : x ? y; } It can be used in classes like this: template<class T, ZEN_REQUIRES(is_integral<T>)> class A { ... }; Or this: template <class T, class Enable = void> class A { ... }; template <class T> class A<T, ZEN_CLASS_REQUIRES(is_integral<T>)> { ... }; template <class T> class A<T, ZEN_CLASS_REQUIRES(is_float<T>)> { ... }; This will all work on C++03 compilers as well. It could also be extended fairly easily to support the trick from Matt Calabrese. Plus, the `FUNCTION_REQUIRES` seems like it could be easily converted to use the `requires` and concept overloading when it gets added to the language as well. What do you think? Thanks, Paul Fultz II