operator name in <functional> proposed name (existence) proposed name (existence and non void return type convertible to something) < less has_operator_less operator_less_has_standard_behaviour
I don't like operator_less_has_standard_behaviour at all. In fact is there really any point to it? Why not simply: has_operator_less<T, R = bool> Where R is the expected return type. In all but a vanishingly small number of cases R will be bool. If you really want to support the "don't care" case for a return type, use has_operator_less<T, dont_care> where "dont_care" is a special placeholder type that you define (could use a better name though?).
+ plus has_operator_plus operator_plus_has_standard_behaviour
These are more complex because we often have mixed mode arithmetic, what about: has_operator_plus<T, U> ? In fact an important use case might be to work out if I can add a T to a U :-) So how about: has_operator_plus<T, U = T, R = dont_care> ? Hard to decide what R should default to in this case, I'm tempted by the "permissive" case of dont_care because it will do the right thing in more mixed arithmetic cases, but the alternative would be to default R to T I guess. Just my 2c, John.