Protected and private inheritance are C++'s equivalent to traits, and they don't suffer from the usual issues of multiple inheritance. As for type classes, check out concepts. By no means am I trying to sell C++, I don't touch it myself, but it doesn't leave you completely adrift in those seas.
In the sense of supporting mixins that don't necessarily pollute your public API. The overlap with other languages isn't perfect, and traits in the stdlib refer to a rather different template-based thing, but I don't think any language has the monopoly on a canon definition of traits. Certainly they're going to be different than traits in Self, which iirc coined the term.
