12 Overloading [over]

12.4 Overloaded operators [over.oper]

12.4.3 Binary operators [over.binary]

12.4.3.1 General [over.binary.general]

A binary operator function is a function named operator@ for a binary operator @ that is either a non-static member function ([class.mfct]) with one parameter or a non-member function with two parameters.
For an expression x @ y with subexpressions x and y, the operator function is selected by overload resolution ([over.match.oper]).
If a member function is selected, the expression is interpreted as
x . operator @ ( y )
Otherwise, if a non-member function is selected, the expression is interpreted as
operator @ ( x , y )
An equality operator function is an operator function for an equality operator ([expr.eq]).
A relational operator function is an operator function for a relational operator ([expr.rel]).
A three-way comparison operator function is an operator function for the three-way comparison operator ([expr.spaceship]).
A comparison operator function is an equality operator function, a relational operator function, or a three-way comparison operator function.