On 2015-06-07 11:41, Evgeny Panasyuk wrote:
07.06.2015 12:07, Roland Bock пишет:
However, this is limited in the way that the type cannot be based on a literal outside a struct/class. There also is a macro that can be employed to create such types, e.g:
SQLPP_ALIAS_PROVIDER(hello);
static_assert( std::is_same<hello_t::_alias_t, sqlpp::char_sequence<'h', 'e', 'l', 'l', 'o', '\000'>>::value, "");
The MACRO cannot be called in a function, though, since local classes must not have static members.
Following code works OK:
int main() { struct specific_compiletime_string { static constexpr const char *value() { return "abc"; } }; static_assert(specific_compiletime_string::value()[0] == 'a', ""); // passes! }
And you can get char sequence in following way: https://github.com/panaseleus/ctte/blob/master/proof_of_concept/proof_of_con...
Very nice, indeed! Using a lambda, I can then do: #define MAKE_CHAR_SEQUENCE(name) \ []() \ { \ struct _intern \ { \ static constexpr const char* value() \ { \ return #name; \ } \ }; \ \ return make_string<_intern, sizeof(#name)>{}; \ }() int main() { auto x = MAKE_CHAR_SEQUENCE(delta); static_assert( std::is_same< decltype(x), sqlpp::char_sequence<'d', 'e', 'l', 't', 'a', '\000'>>::value, ""); } (code attached) Cool, I'll use that. It will allow users to define/use aliases in-place. But: Lamda expressions cannot live in unevaluated code. Thus using X = decltype(MAKE_CHAR_SEQUENCE(delta)); is illegal :-(
Thus, while I assume that it is faster than what happens inside the MPLLIBS_STRING (haven't measured it), its use is more limited, too.
As I understand, complexity of MPLLIBS_STRING comes from fact that it can be passed immediately as template argument.
I guess so, too. MAKE_CHAR_SEQUENCE can be used as a function argument at least :-)