202 lines
7.8 KiB
Markdown
202 lines
7.8 KiB
Markdown
[namespace.constraints]
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# 16 Library introduction [[library]](./#library)
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## 16.4 Library-wide requirements [[requirements]](requirements#namespace.constraints)
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### 16.4.5 Constraints on programs [[constraints]](constraints#namespace.constraints)
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#### 16.4.5.2 Namespace use [namespace.constraints]
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#### [16.4.5.2.1](#namespace.std) Namespace std [[namespace.std]](namespace.std)
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[1](#namespace.std-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L2991)
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Unless otherwise specified,
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the behavior of a C++ program is undefined if it adds declarations or definitions to namespacestd or to a namespace within namespacestd[.](#namespace.std-1.sentence-1)
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[2](#namespace.std-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L2998)
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Unless explicitly prohibited,
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a program may add a template specialization for
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any standard library class template
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to namespacestd provided that
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- [(2.1)](#namespace.std-2.1)
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the added declaration
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depends on at least one program-defined type, and
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- [(2.2)](#namespace.std-2.2)
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the specialization meets the standard library requirements
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for the original template[.](#namespace.std-2.sentence-1)[151](#footnote-151 "Any library code that instantiates other library templates must be prepared to work adequately with any user-supplied specialization that meets the minimum requirements of this document.")
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[3](#namespace.std-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3018)
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The behavior of a C++ program is undefined
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if it declares an explicit or partial specialization
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of any standard library variable template,
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except where explicitly permitted by the specification of that variable template[.](#namespace.std-3.sentence-1)
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[*Note [1](#namespace.std-note-1)*:
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The requirements on an explicit or partial specialization
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are stated by each variable template that grants such permission[.](#namespace.std-3.sentence-2)
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â *end note*]
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[4](#namespace.std-4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3028)
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The behavior of a C++ program is undefined if it declares
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- [(4.1)](#namespace.std-4.1)
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an explicit specialization of any member function of a standard
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library class template, or
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- [(4.2)](#namespace.std-4.2)
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an explicit specialization of any member function template of a
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standard library class or class template, or
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- [(4.3)](#namespace.std-4.3)
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an explicit or partial specialization of any member class template
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of a standard library class or class template, or
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- [(4.4)](#namespace.std-4.4)
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a deduction guide for any standard library class template[.](#namespace.std-4.sentence-1)
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[5](#namespace.std-5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3043)
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A program may explicitly instantiate
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a class template defined in the standard library
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only if the declaration
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- [(5.1)](#namespace.std-5.1)
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depends on the name of at least one program-defined type, and
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- [(5.2)](#namespace.std-5.2)
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the instantiation meets the standard library requirements for the
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original template[.](#namespace.std-5.sentence-1)
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[6](#namespace.std-6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3054)
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Let *F* denote
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a standard library function ([[global.functions]](global.functions "16.4.6.4 Non-member functions")),
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a standard library static member function,
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or an instantiation
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of a standard library function template[.](#namespace.std-6.sentence-1)
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Unless *F* is designated
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an [*addressable function*](#def:function,addressable "16.4.5.2.1 Namespace std [namespace.std]"),
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the behavior of a C++ program is unspecified (possibly ill-formed)
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if it explicitly or implicitly attempts
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to form a pointer
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to *F*[.](#namespace.std-6.sentence-2)
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[*Note [2](#namespace.std-note-2)*:
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Possible means of forming such pointers include
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application of the unary & operator ([[expr.unary.op]](expr.unary.op "7.6.2.2 Unary operators")),addressof ([[specialized.addressof]](specialized.addressof "20.2.11 addressof")),
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or
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a function-to-pointer standard conversion ([[conv.func]](conv.func "7.3.4 Function-to-pointer conversion"))[.](#namespace.std-6.sentence-3)
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â *end note*]
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Moreover,
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the behavior of a C++ program is unspecified (possibly ill-formed)
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if it attempts to form a reference
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to *F* or
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if it attempts to form a pointer-to-member designating
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either a standard library non-static member function ([[member.functions]](member.functions "16.4.6.5 Member functions"))
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or an instantiation of a standard library member function template[.](#namespace.std-6.sentence-4)
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[7](#namespace.std-7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3082)
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Let *F* denote
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a standard library function or function template[.](#namespace.std-7.sentence-1)
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Unless *F* is designated an addressable function,
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it is unspecified if or how
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a reflection value designating the associated entity can be formed[.](#namespace.std-7.sentence-2)
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[*Note [3](#namespace.std-note-3)*:
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For example, it is possible that std::meta::members_of will not return reflections of standard library functions
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that an implementation handles through an extra-linguistic mechanism[.](#namespace.std-7.sentence-3)
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â *end note*]
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[8](#namespace.std-8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3095)
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Let *C* denote
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a standard library class or class template specialization[.](#namespace.std-8.sentence-1)
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It is unspecified if or how
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a reflection value can be formed to any private member of *C*,
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or what the names of such members may be[.](#namespace.std-8.sentence-2)
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[9](#namespace.std-9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3102)
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A translation unit shall not declare namespace std to be an inline namespace ([[namespace.def]](namespace.def "9.9.2 Namespace definition"))[.](#namespace.std-9.sentence-1)
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[151)](#footnote-151)[151)](#footnoteref-151)
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Any
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library code that instantiates other library templates
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must be prepared to work adequately with any user-supplied specialization
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that meets the minimum requirements of this document[.](#footnote-151.sentence-1)
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#### [16.4.5.2.2](#namespace.posix) Namespace posix [[namespace.posix]](namespace.posix)
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[1](#namespace.posix-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3107)
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The behavior of a C++ program is undefined if it adds declarations or definitions to namespaceposix or to a namespace within namespaceposix unless otherwise specified[.](#namespace.posix-1.sentence-1)
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The namespace posix is reserved for use by
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ISO/IEC/IEEE 9945 and other POSIX standards[.](#namespace.posix-1.sentence-2)
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#### [16.4.5.2.3](#namespace.future) Namespaces for future standardization [[namespace.future]](namespace.future)
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[1](#namespace.future-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3117)
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Top-level namespaces whose [*namespace-name*](namespace.def.general#nt:namespace-name "9.9.2.1 General [namespace.def.general]") consists of std followed by one or more [*digit*](lex.name#nt:digit "5.11 Identifiers [lex.name]")*s* ([[lex.name]](lex.name "5.11 Identifiers"))
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are reserved for future standardization[.](#namespace.future-1.sentence-1)
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The behavior of a C++ program is undefined if
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it adds declarations or definitions to such a namespace[.](#namespace.future-1.sentence-2)
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[*Example [1](#namespace.future-example-1)*:
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The top-level namespace std2 is reserved
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for use by future revisions of this International Standard[.](#namespace.future-1.sentence-3)
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â *end example*]
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