[special]

# 11 Classes [[class]](./#class)

## 11.4 Class members [[class.mem]](class.mem#special)

### 11.4.4 Special member functions [special]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1154)

Default constructors ([[class.default.ctor]](class.default.ctor "11.4.5.2 Default constructors")),
copy constructors, move constructors ([[class.copy.ctor]](class.copy.ctor "11.4.5.3 Copy/move constructors")),
copy assignment operators, move assignment operators ([[class.copy.assign]](class.copy.assign "11.4.6 Copy/move assignment operator")),
and prospective destructors ([[class.dtor]](class.dtor "11.4.7 Destructors")) are[*special member functions*](#def:special_member_functions)[.](#1.sentence-1)

[*Note [1](#note-1)*:

The implementation will implicitly declare these member functions for some class
types when the program does not explicitly declare them[.](#1.sentence-2)

The implementation will implicitly define them
as needed ([[dcl.fct.def.default]](dcl.fct.def.default "9.6.2 Explicitly-defaulted functions"))[.](#1.sentence-3)

— *end note*]

An implicitly-declared special member function is declared at the closing} of the [*class-specifier*](class.pre#nt:class-specifier "11.1 Preamble [class.pre]")[.](#1.sentence-4)

Programs shall not define implicitly-declared special member functions[.](#1.sentence-5)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1175)

Programs may explicitly refer to implicitly-declared special member functions[.](#2.sentence-1)

[*Example [1](#example-1)*:

A program may explicitly call or form a pointer to member
to an implicitly-declared special member function[.](#2.sentence-2)

struct A { }; // implicitly declared A​::​operator=struct B : A { B& operator=(const B &);};
B& B::operator=(const B& s) {this->A::operator=(s); // well-formedreturn *this;} — *end example*]

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1193)

[*Note [2](#note-2)*:

The special member functions affect the way objects of class type are created,
copied, moved, and destroyed, and how values can be converted to values of other types[.](#3.sentence-1)

Often such special member functions are called implicitly[.](#3.sentence-2)

— *end note*]

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1200)

Special member functions obey the usual access rules ([[class.access]](class.access "11.8 Member access control"))[.](#4.sentence-1)

[*Example [2](#example-2)*:

Declaring a constructor protected
ensures that only derived classes and friends can create objects using it[.](#4.sentence-2)

— *end example*]

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1208)

Two special member functions are of the same kind if

- [(5.1)](#5.1)

they are both default constructors,

- [(5.2)](#5.2)

they are both copy or move constructors
with the same first parameter type, or

- [(5.3)](#5.3)

they are both copy or move assignment operators
with the same first parameter type
and the same [*cv-qualifier*](dcl.decl.general#nt:cv-qualifier "9.3.1 General [dcl.decl.general]")*s* and [*ref-qualifier*](dcl.decl.general#nt:ref-qualifier "9.3.1 General [dcl.decl.general]"), if any[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1219)

An [*eligible special member function*](#def:special_member_function,eligible "11.4.4 Special member functions [special]") is a special member function for which:

- [(6.1)](#6.1)

the function is not deleted,

- [(6.2)](#6.2)

the associated constraints ([[temp.constr]](temp.constr "13.5 Template constraints")), if any, are satisfied, and

- [(6.3)](#6.3)

no special member function of the same kind
whose associated constraints, if any, are satisfied
is more constrained ([[temp.constr.order]](temp.constr.order "13.5.5 Partial ordering by constraints"))[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L1229)

For a class, its non-static data members, its non-virtual direct base classes,
and, if the class is not abstract ([[class.abstract]](class.abstract "11.7.4 Abstract classes")), its virtual base
classes are called its [*potentially constructed subobjects*](#def:potentially_constructed_subobjects)[.](#7.sentence-1)