[boost] Adding helpful requires macros to the enable_if utility

Subject: [boost] Adding helpful requires macros to the enable_if utility
From: paul Fultz (pfultz2_at_[hidden])
Date: 2014-06-27 12:10:33

These following set of macros, I have found very useful in C++:

#define BOOST_ERROR_PARENTHESIS_MUST_BE_PLACED_AROUND_THE_RETURN_TYPE(...) __VA_ARGS__>::type
#define BOOST_FUNCTION_REQUIRES(...) typename boost::enable_if_c<(__VA_ARGS__), BOOST_ERROR_PARENTHESIS_MUST_BE_PLACED_AROUND_THE_RETURN_TYPE

#define BOOST_CLASS_REQUIRES(...) typename boost::enable_if_c<(__VA_ARGS__)>::type

#define BOOST_REQUIRES(...) typename boost::enable_if_c<(__VA_ARGS__), int>::type = 0

Which I use like the following

For functions:

    template <class T>
    BOOST_FUNCTION_REQUIRES(boost::is_arithmetic<T>::value) 
    (T) foo(T t) { return t; }

And C++11 functions:

    template <class T, BOOST_REQUIRES(boost::is_arithmetic<T>())>
    T foo(T t) { return t; }

Class specializations:

    template <class T, class Enable = void> 
    class A { ... };

    template <class T>
    class A<T, BOOST_CLASS_REQUIRES(is_integral<T>())> { ... };

    template <class T>
    class A<T, BOOST_CLASS_REQUIRES(is_float<T>())> { ... };


It would be nice if these were the added with the enable_if utility with boost.

Thanks,
Paul