I find the use of macros to be far more readable than the direct use of templates. In fact, I was earlier toying with the idea of writing such macros myself. Needless to say that I would find them to be very helpful.
Besides readability, they actually help avoid the most vexing parse in C++(something template aliases can't fix).
Paul, can the concept be extended to a DSEL-like utility?
Well you can already write something like this on compilers that support
`constexpr`:
template <class T>
BOOST_FUNCTION_REQUIRES(is_foo<T>() and is_bar<T>())
(T) foo(T t) { return t; }
This could be made to work on older compilers by using expression templates,
but
then using literals such as `is_foo<T>::value` would fail. Perhaps a second
macro like `BOOST_FUNCTION_REQUIRES_E` could be written to help avoid the
confusion. Plus, having separate `_E` macros can actually still be useful in
C++11 because of limitations of `constexpr`. For example, say we use a
`trait`
function that deduces the type parameters from a variable:
template