12 Overloading [over]

12.6 Overloaded operators [over.oper]

12.6.2 Binary operators [over.binary]

1
#
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 )
2
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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.

12.6.2.1 Simple assignment [over.ass]

1
#
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
:
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
]
2
#
[Note
:
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
]
3
#
[Note
:
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
: 
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
]