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>
It would be: has_operator_less<T, U, R=bool> as we said in previous discussion we want to address the case where we compare T with U!=T.
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?).
the "don't care" case was a strong requirement from previous discussion. I like your proposed solution has_operator_less<T, U, dont_care> dont_care would have to be an empty class maybe boost::type_traits::dont_care?
+ plus has_operator_plus
These are more complex because we often have mixed mode arithmetic, what about: has_operator_plus<T, U> ?
right, that is what I meant
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.
I am in favor of dont_care Frédéric