!= auto generated from == in C++20?

Question

Is this standard behavior in C++20? I couldn't find anything about it in cppreference.

I've just tried both on Clang and on Visual Studio and it works and it doesn't give me any sort of error or warning. I also checked with the debugger to see if operator== was being called and it was! Does C++20 now allows for the automatic generation of operator!= when operator== is present? Does it default to a sane !(a == b)? If that's so, then that's awesome for C++!

Answer 1

!= auto generated from == in C++20?

Is this standard behavior in C++20?

Yes. operator!= is auto generated from operator== in C++20.

Furthermore, all four relational operators are generated if you define operator<=>, and all of the comparison operators are generated if you define operator<=> as defaulted.

What you want to do in most cases:

struct example
{
    std::string a;
    int         b;

    auto operator<=>(const example&) const = default;
};