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.

12.4.3.2 Simple assignment [over.ass]

A simple assignment operator function is a binary operator function named operator=.
A simple assignment operator function shall be a non-static member function.
[Note 1:
Because only standard conversion sequences are considered when converting to the left operand of an assignment operation ([over.best.ics]), an expression x = y with a subexpression x of class type is always interpreted as x.operator=(y).
— end note]
[Note 2:
Since a copy assignment operator is implicitly declared for a class if not declared by the user ([class.copy.assign]), a base class assignment operator function is always hidden by the copy assignment operator function of the derived class.
— end note]
[Note 3:
Any assignment operator function, even the copy and move assignment operators, can be virtual.
For a derived class D with a base class B for which a virtual copy/move assignment has been declared, the copy/move assignment operator in D does not override B's virtual copy/move assignment operator.
[Example 1: struct B { virtual int operator= (int); virtual B& operator= (const B&); }; struct D : B { virtual int operator= (int); virtual D& operator= (const B&); }; D dobj1; D dobj2; B* bptr = &dobj1; void f() { bptr->operator=(99); // calls D​::​operator=(int) *bptr = 99; // ditto bptr->operator=(dobj2); // calls D​::​operator=(const B&) *bptr = dobj2; // ditto dobj1 = dobj2; // calls implicitly-declared D​::​operator=(const D&) } — end example]
— end note]