[over.binary]

# 12 Overloading [[over]](./#over)

## 12.4 Overloaded operators [[over.oper]](over.oper#over.binary)

### 12.4.3 Binary operators [over.binary]

#### [12.4.3.1](#general) General [[over.binary.general]](over.binary.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L3530)

A [*binary operator function*](#def:operator_function,binary "12.4.3.1 General [over.binary.general]") is a function named operator@ for a binary operator @ that is either
a non-static member function ([[class.mfct]](class.mfct "11.4.2 Member functions")) with one non-object parameter or
a non-member function with two parameters[.](#general-1.sentence-1)

For an expression x @ y with subexpressions x and y,
the operator function is selected by overload resolution ([[over.match.oper]](over.match.oper "12.2.2.3 Operators in expressions"))[.](#general-1.sentence-2)

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](#general-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L3550)

An [*equality operator function*](#def:operator_function,equality "12.4.3.1 General [over.binary.general]") is an operator function
for an equality operator ([[expr.eq]](expr.eq "7.6.10 Equality operators"))[.](#general-2.sentence-1)

A [*relational operator function*](#def:operator_function,relational "12.4.3.1 General [over.binary.general]") is an operator function
for a relational operator ([[expr.rel]](expr.rel "7.6.9 Relational operators"))[.](#general-2.sentence-2)

A [*three-way comparison operator function*](#def:operator_function,three-way_comparison "12.4.3.1 General [over.binary.general]") is an operator function
for the three-way comparison operator ([[expr.spaceship]](expr.spaceship "7.6.8 Three-way comparison operator"))[.](#general-2.sentence-3)

A [*comparison operator function*](#def:operator_function,comparison "12.4.3.1 General [over.binary.general]") is
an equality operator function,
a relational operator function, or
a three-way comparison operator function[.](#general-2.sentence-4)

#### [12.4.3.2](#over.assign) Simple assignment [[over.assign]](over.assign)

[1](#over.assign-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L3566)

A [*simple assignment operator function*](#def:operator_function,simple_assignment "12.4.3.2 Simple assignment [over.assign]") is a binary operator function named operator=[.](#over.assign-1.sentence-1)

A simple assignment operator function shall be a non-static member function[.](#over.assign-1.sentence-2)

[*Note [1](#over.assign-note-1)*:

Because only standard conversion sequences are considered when converting
to the left operand of an assignment operation ([[over.best.ics]](over.best.ics "12.2.4.2 Implicit conversion sequences")),
an expression x = y with a subexpression x of class type
is always interpreted as x.operator=(y)[.](#over.assign-1.sentence-3)

— *end note*]

[2](#over.assign-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L3577)

[*Note [2](#over.assign-note-2)*:

Since a copy assignment operator is implicitly declared for a class
if not declared by the user ([[class.copy.assign]](class.copy.assign "11.4.6 Copy/move assignment operator")),
a base class assignment operator function is always hidden by
the copy assignment operator function of the derived class[.](#over.assign-2.sentence-1)

— *end note*]

[3](#over.assign-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L3585)

[*Note [3](#over.assign-note-3)*:

Any assignment operator function, even the copy and move assignment operators,
can be virtual[.](#over.assign-3.sentence-1)

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 overrideB's virtual copy/move assignment operator[.](#over.assign-3.sentence-2)

[*Example [1](#over.assign-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*]