Why is operator!= removed in C++20 for many standard library types?
In C++20 the way that the relational operators work was changed, notably with the introduction of the spaceship <=> operator. In particular, If you only provide operator==, then a != b is rewritten to !(a == b). From [over.match.oper]/3.4: The rewritten candidate set is determined as follows: For the relational ([expr.rel]) operators, the rewritten candidates … Read more