[boost] How to determine if a function with a given signature is declared?

Subject: [boost] How to determine if a function with a given signature is declared?
From: andrew.beck_at_[hidden]
Date: 2011-05-17 08:40:14

Hi,
Newbie question follows...

I've used BOOST_MPL_HAS_XXX_TRAIT_DEF in the past but recently needed to
determine if a function was defined with a given signature. Searching
boost::mpl, stackoverflow etc, I couldn't find anything to do what I
needed. I've attached my solution below. Basically, I'm wondering if there
is a boost::mpl solution or some other more elegant solution.

thanks,
andrew

#include <boost/mpl/bool.hpp>
#include <boost/mpl/assert.hpp>

#define XXX_DEFINED(symbol) \
    template <typename T, T* = symbol> \
    struct check_ ## symbol \
    { \
        typedef void type; \
    }; \
 \
    template <typename T, typename enable = void> \
    struct symbol ## _defined : \
        boost::mpl::false_ \
    { }; \
 \
    template <typename T> \
    struct symbol ## _defined<T, typename check_ ## symbol<T>::type > : \
        boost::mpl::true_ \
    { };

// declare a some_func(int) so we can see if its declared...
void some_func(int)
{}

// defines some_func_defined template
XXX_DEFINED(some_func);

BOOST_MPL_ASSERT(( some_func_defined<void(int)> ));

// some_func(double) hasn't been declared
BOOST_MPL_ASSERT_NOT(( some_func_defined<void(double)> ));