Re: [boost] [optional] operator<(optional<T>, T) -- is it wrong?

Regular is a concept. See Stepanov's Elements of Programming. Or just think "int". ie assignable, copyable, copies are disjoint, etc. Stepanov includes ordering as part of Regular (IIRC).

P.S. One of the important parts of Regular: it is what the STL typically assumes. In Stepanov's world (almost) all types are Regular. (not that he thinks everything is Regular, but that all the good things are :-) ie he dislikes and avoids anything that isn't. Non-Regular should be the rare exception. you should strive to make your class Regular.)