Re: [Boost-users] [has_xxx] How can it work at all???

Alexander Nasonov <alnsn <at> yandex.ru> writes:

struct Cases { template<class N> void operator()(N) const { ... }

void operator()(default_t) const { ... } };

The trick posted on RSDN lets me check whether the last call operator exists and take this into account.

One useful generalisation of this trick is something like

result_of_with_default<void (Cases)(default_t), no_default_case>

In order for the above to work, Cases::operator()(N) must be more specialised: struct Cases { template<int N> void operator()(mpl::int_<N>) const { ... } // void operator()(default_t) const { ... } }; So, result_of_with_default<Cases(default_t), no_default_case>::type would be no_default_case. Alex