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cppdraft/locale/facet.md

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+[locale.facet]
+
+# 28 Text processing library [[text]](./#text)
+
+## 28.3 Localization library [[localization]](localization#locale.facet)
+
+### 28.3.3 Locales [[locales]](locales#locale.facet)
+
+#### 28.3.3.1 Class locale [[locale]](locale#facet)
+
+#### 28.3.3.1.2 Types [[locale.types]](locale.types#locale.facet)
+
+#### 28.3.3.1.2.2 Class locale​::​facet [locale.facet]
+
+[🔗](#lib:locale,facet)
+
+namespace std {class locale::facet {protected:explicit facet(size_t refs = 0); virtual ~facet();
+ facet(const facet&) = delete; void operator=(const facet&) = delete; };}
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L766)
+
+Class facet is the base class for locale feature sets[.](#1.sentence-1)
+
+A class is a [*facet*](#def:facet "28.3.3.1.2.2 Class locale​::​facet [locale.facet]") if it is publicly derived from another facet, or
+if it is a class derived from locale​::​facet and
+contains a publicly accessible declaration as follows:[215](#footnote-215 "This is a complete list of requirements; there are no other requirements. Thus, a facet class need not have a public copy constructor, assignment, default constructor, destructor, etc.")static ::std::locale::id id;
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L781)
+
+Template parameters in this Clause
+which are required to be facets
+are those named Facet in declarations[.](#2.sentence-1)
+
+A program that passes
+a type that is *not* a facet, or
+a type that refers to a volatile-qualified facet,
+as an (explicit or deduced) template parameter to
+a locale function expecting a facet,
+is ill-formed[.](#2.sentence-2)
+
+A const-qualified facet is a valid template argument to
+any locale function that expects a Facet template parameter[.](#2.sentence-3)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L794)
+
+The refs argument to the constructor is used for lifetime management[.](#3.sentence-1)
+
+For refs == 0,
+the implementation performs delete static_cast<locale​::​facet*>(f) (where f is a pointer to the facet)
+when the last locale object containing the facet is destroyed;
+for refs == 1, the implementation never destroys the facet[.](#3.sentence-2)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L802)
+
+Constructors of all facets defined in this Clause
+take such an argument and pass it along to
+their facet base class constructor[.](#4.sentence-1)
+
+All one-argument constructors defined in this Clause are explicit,
+preventing their participation in implicit conversions[.](#4.sentence-2)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L809)
+
+For some standard facets a standard “…_byname” class,
+derived from it, implements the virtual function semantics
+equivalent to that facet of the locale
+constructed by locale(const char*) with the same name[.](#5.sentence-1)
+
+Each such facet provides a constructor that takes
+a const char* argument, which names the locale, and
+a refs argument, which is passed to the base class constructor[.](#5.sentence-2)
+
+Each such facet also provides a constructor that takes
+a string argument str and
+a refs argument,
+which has the same effect as calling the first constructor
+with the two arguments str.c_str() and refs[.](#5.sentence-3)
+
+If there is no “…_byname” version of a facet,
+the base class implements named locale semantics itself
+by reference to other facets[.](#5.sentence-4)
+
+[215)](#footnote-215)[215)](#footnoteref-215)
+
+This is a complete list of requirements; there are no other requirements[.](#footnote-215.sentence-1)
+
+Thus, a facet class need not have a public
+copy constructor, assignment, default constructor, destructor, etc[.](#footnote-215.sentence-2)