John M. Dlugosz writes:
[...]
The trait will be false by default, and I'd declare something to nominate
types that should be seen to have that trait. I want it to follow
inheritance; if B has been declared to be in my category, and C is derived
from B, then C will also be in that category without needing to do anything
more (though some way to turn it _off_ would be available).
This may or may not be what you're looking for:
#include
struct make_pretty { };
std::true_type is_pretty_impl(make_pretty*);
std::false_type is_pretty_impl(...);
template <typename T>
struct is_pretty : decltype(is_pretty_impl((T*)nullptr)) { };
struct pretty : make_pretty { };
struct pretty_too : pretty { };
struct ugly_by_default;
struct pretty_can_be_made_ugly : make_pretty { };
template <> struct is_pretty
: std::false_type
{ };
static_assert(is_pretty<pretty>::value, "");
static_assert(is_pretty::value, "");
static_assert(!is_pretty::value, "");
static_assert(!is_pretty::value, "");
Caveat: is_pretty will return false on a type that inherits something
pretty until it is complete (this could be confusing).
Regards,
Louis Dionne
