c++ less operator overload, which way to use?

Question

For example: in a C++ header file, if I defined a struct Record and I would like to use it for possible sorting so that I want to overload the less operator

Answer 1

Favor in-class unless it cannot be in-class because first argument is the wrong type.

Answer 2

The best way to define the less operator is:

struct Record{
    (...)
    const bool operator < ( const Record &r ) const{
        return ( num < r.num );
    }
};

Answer 3

They are essentially the same, other than the first being non-const and allowing you to modify itself.

I prefer the second for 2 reasons:

1. It doesn't have to be a friend.
2. lhs does not have to be a Record