[namespace.def] - C++17 → C++20

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@@ -13,46 +13,46 @@ namespace-definition:
         nested-namespace-definition
 ```
 ``` bnf
 named-namespace-definition:
- 'inline'ₒₚₜ 'namespace' attribute-specifier-seqₒₚₜ identifier '{' namespace-body '}'
 ```
 ``` bnf
 unnamed-namespace-definition:
- 'inline'ₒₚₜ 'namespace' attribute-specifier-seqₒₚₜ '{' namespace-body '}'
 ```
 ``` bnf
 nested-namespace-definition:
- 'namespace' enclosing-namespace-specifier '::' identifier '{' namespace-body '}'
 ```
 ``` bnf
 enclosing-namespace-specifier:
         identifier
-        enclosing-namespace-specifier '::' identifier
 ```
 ``` bnf
 namespace-body:
         declaration-seqₒₚₜ
 ```
-Every *namespace-definition* shall appear in the global scope or in a
-namespace scope ([[basic.scope.namespace]]).
 In a *named-namespace-definition*, the *identifier* is the name of the
-namespace. If the *identifier*, when looked up (
-[[basic.lookup.unqual]]), refers to a *namespace-name* (but not a
-*namespace-alias*) that was introduced in the namespace in which the
-*named-namespace-definition* appears or that was introduced in a member
-of the inline namespace set of that namespace, the
-*namespace-definition* *extends* the previously-declared namespace.
-Otherwise, the *identifier* is introduced as a *namespace-name* into the
-declarative region in which the *named-namespace-definition* appears.
 Because a *namespace-definition* contains *declaration*s in its
 *namespace-body* and a *namespace-definition* is itself a *declaration*,
 it follows that *namespace-definition*s can be nested.
@@ -106,22 +106,22 @@ The optional *attribute-specifier-seq* in a *named-namespace-definition*
 appertains to the namespace being defined or extended.
 Members of an inline namespace can be used in most respects as though
 they were members of the enclosing namespace. Specifically, the inline
 namespace and its enclosing namespace are both added to the set of
-associated namespaces used in argument-dependent lookup (
-[[basic.lookup.argdep]]) whenever one of them is, and a
-*using-directive* ([[namespace.udir]]) that names the inline namespace
-is implicitly inserted into the enclosing namespace as for an unnamed
-namespace ([[namespace.unnamed]]). Furthermore, each member of the
-inline namespace can subsequently be partially specialized (
-[[temp.class.spec]]), explicitly instantiated ([[temp.explicit]]), or
-explicitly specialized ([[temp.expl.spec]]) as though it were a member
-of the enclosing namespace. Finally, looking up a name in the enclosing
-namespace via explicit qualification ([[namespace.qual]]) will include
-members of the inline namespace brought in by the *using-directive* even
-if there are declarations of that name in the enclosing namespace.
 These properties are transitive: if a namespace `N` contains an inline
 namespace `M`, which in turn contains an inline namespace `O`, then the
 members of `O` can be used as though they were members of `M` or `N`.
 The *inline namespace set* of `N` is the transitive closure of all
@@ -132,26 +132,29 @@ namespaces.
 A *nested-namespace-definition* with an *enclosing-namespace-specifier*
 `E`, *identifier* `I` and *namespace-body* `B` is equivalent to
 ``` cpp
-namespace E { namespace I { B } }
 ```
 [*Example 3*:
 ``` cpp
-namespace A::B::C {
   int i;
 }
 ```
 The above has the same effect as:
 ``` cpp
 namespace A {
-  namespace B {
     namespace C {
       int i;
     }
   }
 }
@@ -162,21 +165,21 @@ namespace A {
 #### Unnamed namespaces <a id="namespace.unnamed">[[namespace.unnamed]]</a>
 An *unnamed-namespace-definition* behaves as if it were replaced by
 ``` bnf
-'inline'ₒₚₜ 'namespace' 'unique ' '{ /* empty body */ }'
-'using namespace' 'unique ' ';'
-'namespace' 'unique ' '{' namespace-body '}'
 ```
 where `inline` appears if and only if it appears in the
-*unnamed-namespace-definition* and all occurrences of `unique ` in a
 translation unit are replaced by the same identifier, and this
 identifier differs from all other identifiers in the translation unit.
 The optional *attribute-specifier-seq* in the
-*unnamed-namespace-definition* appertains to `unique `.
 [*Example 1*:
 ``` cpp
 namespace { int i; }            // unique::i
@@ -201,19 +204,19 @@ void h() {
 — *end example*]
 #### Namespace member definitions <a id="namespace.memdef">[[namespace.memdef]]</a>
 A declaration in a namespace `N` (excluding declarations in nested
-scopes) whose *declarator-id* is an *unqualified-id* ([[dcl.meaning]]),
-whose *class-head-name* (Clause [[class]]) or *enum-head-name* (
-[[dcl.enum]]) is an *identifier*, or whose *elaborated-type-specifier*
-is of the form *class-key* *attribute-specifier-seq*ₒₚₜ  *identifier* (
-[[dcl.type.elab]]), or that is an *opaque-enum-declaration*, declares
-(or redeclares) its *unqualified-id* or *identifier* as a member of `N`.
-[*Note 1*: An explicit instantiation ([[temp.explicit]]) or explicit
-specialization ([[temp.expl.spec]]) of a template does not introduce a
 name and thus may be declared using an *unqualified-id* in a member of
 the enclosing namespace set, if the primary template is declared in an
 inline namespace. — *end note*]
 [*Example 1*:
@@ -231,14 +234,14 @@ namespace X {
 ```
 — *end example*]
 Members of a named namespace can also be defined outside that namespace
-by explicit qualification ([[namespace.qual]]) of the name being
-defined, provided that the entity being defined was already declared in
-the namespace and the definition appears after the point of declaration
-in a namespace that encloses the declaration’s namespace.
 [*Example 2*:
 ``` cpp
 namespace Q {
@@ -257,32 +260,32 @@ namespace R {
 }
 ```
 — *end example*]
-If a `friend` declaration in a non-local class first declares a class,
-function, class template or function template[^5] the friend is a member
-of the innermost enclosing namespace. The `friend` declaration does not
-by itself make the name visible to unqualified lookup (
-[[basic.lookup.unqual]]) or qualified lookup ([[basic.lookup.qual]]).
 [*Note 2*: The name of the friend will be visible in its namespace if a
 matching declaration is provided at namespace scope (either before or
 after the class definition granting friendship). — *end note*]
 If a friend function or function template is called, its name may be
 found by the name lookup that considers functions from namespaces and
-classes associated with the types of the function arguments (
-[[basic.lookup.argdep]]). If the name in a `friend` declaration is
-neither qualified nor a *template-id* and the declaration is a function
-or an *elaborated-type-specifier*, the lookup to determine whether the
-entity has been previously declared shall not consider any scopes
-outside the innermost enclosing namespace.
-[*Note 3*: The other forms of `friend` declarations cannot declare a
-new member of the innermost enclosing namespace and thus follow the
-usual lookup rules. — *end note*]
 [*Example 3*:
 ``` cpp
 // Assume f and g have not yet been declared.

         nested-namespace-definition
 ```
 ``` bnf
 named-namespace-definition:
+        inlineₒₚₜ namespace attribute-specifier-seqₒₚₜ identifier '{' namespace-body '}'
 ```
 ``` bnf
 unnamed-namespace-definition:
+        inlineₒₚₜ namespace attribute-specifier-seqₒₚₜ '{' namespace-body '}'
 ```
 ``` bnf
 nested-namespace-definition:
+        namespace enclosing-namespace-specifier '::' inlineₒₚₜ identifier '{' namespace-body '}'
 ```
 ``` bnf
 enclosing-namespace-specifier:
         identifier
+        enclosing-namespace-specifier '::' inlineₒₚₜ identifier
 ```
 ``` bnf
 namespace-body:
         declaration-seqₒₚₜ
 ```
+Every *namespace-definition* shall appear at namespace scope
+[[basic.scope.namespace]].
 In a *named-namespace-definition*, the *identifier* is the name of the
+namespace. If the *identifier*, when looked up [[basic.lookup.unqual]],
+refers to a *namespace-name* (but not a *namespace-alias*) that was
+introduced in the namespace in which the *named-namespace-definition*
+appears or that was introduced in a member of the inline namespace set
+of that namespace, the *namespace-definition* *extends* the
+previously-declared namespace. Otherwise, the *identifier* is introduced
+as a *namespace-name* into the declarative region in which the
+*named-namespace-definition* appears.
 Because a *namespace-definition* contains *declaration*s in its
 *namespace-body* and a *namespace-definition* is itself a *declaration*,
 it follows that *namespace-definition*s can be nested.
 appertains to the namespace being defined or extended.
 Members of an inline namespace can be used in most respects as though
 they were members of the enclosing namespace. Specifically, the inline
 namespace and its enclosing namespace are both added to the set of
+associated namespaces used in argument-dependent lookup
+[[basic.lookup.argdep]] whenever one of them is, and a *using-directive*
+[[namespace.udir]] that names the inline namespace is implicitly
+inserted into the enclosing namespace as for an unnamed namespace
+[[namespace.unnamed]]. Furthermore, each member of the inline namespace
+can subsequently be partially specialized [[temp.class.spec]],
+explicitly instantiated [[temp.explicit]], or explicitly specialized
+[[temp.expl.spec]] as though it were a member of the enclosing
+namespace. Finally, looking up a name in the enclosing namespace via
+explicit qualification [[namespace.qual]] will include members of the
+inline namespace brought in by the *using-directive* even if there are
+declarations of that name in the enclosing namespace.
 These properties are transitive: if a namespace `N` contains an inline
 namespace `M`, which in turn contains an inline namespace `O`, then the
 members of `O` can be used as though they were members of `M` or `N`.
 The *inline namespace set* of `N` is the transitive closure of all
 A *nested-namespace-definition* with an *enclosing-namespace-specifier*
 `E`, *identifier* `I` and *namespace-body* `B` is equivalent to
 ``` cpp
+namespace E { \opt{inline} namespace I { B } }
 ```
+where the optional `inline` is present if and only if the *identifier*
+`I` is preceded by `inline`.
 [*Example 3*:
 ``` cpp
+namespace A::inline B::C {
   int i;
 }
 ```
 The above has the same effect as:
 ``` cpp
 namespace A {
+ inline namespace B {
     namespace C {
       int i;
     }
   }
 }
 #### Unnamed namespaces <a id="namespace.unnamed">[[namespace.unnamed]]</a>
 An *unnamed-namespace-definition* behaves as if it were replaced by
 ``` bnf
+inlineₒₚₜ namespace unique '{' '/* empty body */' '}'
+using namespace unique ';'
+namespace unique '{' namespace-body '}'
 ```
 where `inline` appears if and only if it appears in the
+*unnamed-namespace-definition* and all occurrences of *`unique`* in a
 translation unit are replaced by the same identifier, and this
 identifier differs from all other identifiers in the translation unit.
 The optional *attribute-specifier-seq* in the
+*unnamed-namespace-definition* appertains to *`unique`*.
 [*Example 1*:
 ``` cpp
 namespace { int i; }            // unique::i
 — *end example*]
 #### Namespace member definitions <a id="namespace.memdef">[[namespace.memdef]]</a>
 A declaration in a namespace `N` (excluding declarations in nested
+scopes) whose *declarator-id* is an *unqualified-id* [[dcl.meaning]],
+whose *class-head-name* [[class.pre]] or *enum-head-name* [[dcl.enum]]
+is an *identifier*, or whose *elaborated-type-specifier* is of the form
+*class-key* *attribute-specifier-seq*ₒₚₜ  *identifier*
+[[dcl.type.elab]], or that is an *opaque-enum-declaration*, declares (or
+redeclares) its *unqualified-id* or *identifier* as a member of `N`.
+[*Note 1*: An explicit instantiation [[temp.explicit]] or explicit
+specialization [[temp.expl.spec]] of a template does not introduce a
 name and thus may be declared using an *unqualified-id* in a member of
 the enclosing namespace set, if the primary template is declared in an
 inline namespace. — *end note*]
 [*Example 1*:
 ```
 — *end example*]
 Members of a named namespace can also be defined outside that namespace
+by explicit qualification [[namespace.qual]] of the name being defined,
+provided that the entity being defined was already declared in the
+namespace and the definition appears after the point of declaration in a
+namespace that encloses the declaration’s namespace.
 [*Example 2*:
 ``` cpp
 namespace Q {
 }
 ```
 — *end example*]
+If a friend declaration in a non-local class first declares a class,
+function, class template or function template[^10] the friend is a
+member of the innermost enclosing namespace. The friend declaration does
+not by itself make the name visible to unqualified lookup
+[[basic.lookup.unqual]] or qualified lookup [[basic.lookup.qual]].
 [*Note 2*: The name of the friend will be visible in its namespace if a
 matching declaration is provided at namespace scope (either before or
 after the class definition granting friendship). — *end note*]
 If a friend function or function template is called, its name may be
 found by the name lookup that considers functions from namespaces and
+classes associated with the types of the function arguments
+[[basic.lookup.argdep]]. If the name in a friend declaration is neither
+qualified nor a *template-id* and the declaration is a function or an
+*elaborated-type-specifier*, the lookup to determine whether the entity
+has been previously declared shall not consider any scopes outside the
+innermost enclosing namespace.
+[*Note 3*: The other forms of friend declarations cannot declare a new
+member of the innermost enclosing namespace and thus follow the usual
+lookup rules. — *end note*]
 [*Example 3*:
 ``` cpp
 // Assume f and g have not yet been declared.

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