Why does boost::variant not provide operator !=

boost-variant, c++

Solution

I think it's just not added to the library. The Boost.Operators won't really help, because either variant would have been derived from boost::operator::equality_comparable. David Pierre is right to say you can use that, but your response is correct too, that the new operator!= won't be found by ADL, so you'll need a using operator.

I'd ask this on the boost-users mailing list.

Edit from @AFoglia's comment:

Seven months later, and I'm studying Boost.Variant, and I stumble over this better explanation of the omission lists.

http://boost.org/Archives/boost/2006/06/105895.php

`operator==` calls `operator==` for the actual class currently in the variant. Likewise calling `operator!=` should also call `operator!=` of the class. (Because, theoretically, a class can be defined so `a!=b` is not the same as `!(a==b)`.) So that would add another requirement that the classes in the variant have an `operator!=`. (There is a debate over whether you can make this assumption in the mailing list thread.)

Problem

Original source