[C++] cool niche template stuff

delimiter_ctype.h

struct delimiter_ctype : std::ctype<char> {
    static const mask* make_table(std::string delims) {
        // make a copy of the "C" locale table
        static std::vector<mask> v(classic_table(), classic_table() + table_size);
        for(mask m : v) {
            m &= ~space;
        }
        for(char d : delims) {
            v[d] |= space;
        }
        return &v[0];
    }
    delimiter_ctype(std::string delims, ::size_t refs = 0) 
        : ctype(make_table(delims), false, refs) {}
};

void foo() {
    std::string line;
    std::stringstream ssline;
    ssline.imbue(std::locale(ssline.getloc(),new delimiter_ctype(",")));
}

has_a.cpp

#include <type_traits>
#define DECLARE_HASA(what) \
template<typename T, typename = int> struct has_##what : std::false_type { };\
template<typename T> struct has_##what<T, decltype((void) T::what, 0)> : std::true_type {};
DECLARE_HASA(when) //declares above statement with 'when' replacing 'what'