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cppdraft/special.md

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+[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)