[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)