From Jason Turner

[module.interface]

C++20 → C++23 6.5 KB 101 lines
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@@ -1,34 +1,37 @@
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  ## Export declaration <a id="module.interface">[[module.interface]]</a>
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  ``` bnf
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  export-declaration:
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- export declaration
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  export '{' declaration-seqₒₚₜ '}'
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  export-keyword module-import-declaration
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  ```
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- An *export-declaration* shall appear only at namespace scope and only in
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  the purview of a module interface unit. An *export-declaration* shall
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  not appear directly or indirectly within an unnamed namespace or a
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  *private-module-fragment*. An *export-declaration* has the declarative
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- effects of its *declaration*, *declaration-seq* (if any), or
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- *module-import-declaration*. An *export-declaration* does not establish
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- a scope and its *declaration* or *declaration-seq* shall not contain an
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- *export-declaration* or *module-import-declaration*.
 
 
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- A declaration is *exported* if it is
 
 
 
 
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- - a namespace-scope declaration declared within an *export-declaration*,
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- or
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  - a *namespace-definition* that contains an exported declaration, or
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  - a declaration within a header unit [[module.import]] that introduces
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  at least one name.
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- An exported declaration that is not a *module-import-declaration* shall
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- declare at least one name. If the declaration is not within a header
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- unit, it shall not declare a name with internal linkage.
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  [*Example 1*:
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  Source file \`"a.h"\`
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@@ -41,27 +44,24 @@ Translation unit #1
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  ``` cpp
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  module;
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  #include "a.h" // error: declaration of x is not in the
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  // purview of a module interface unit
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  export module M;
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- export namespace {} // error: does not introduce any names
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- export namespace {
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- int a1; // error: export of name with internal linkage
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- }
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  namespace {
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  export int a2; // error: export of name with internal linkage
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  }
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  export static int b; // error: b explicitly declared static
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  export int f(); // OK
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  export namespace N { } // OK
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- export using namespace N; // error: does not declare a name
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  ```
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  — *end example*]
60
 
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- If the declaration is a *using-declaration* [[namespace.udecl]] and is
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- not within a header unit, all entities to which all of the
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  *using-declarator*s ultimately refer (if any) shall have been introduced
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  with a name having external linkage.
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  [*Example 2*:
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@@ -102,11 +102,11 @@ namespace N {
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  export using N::h; // error: #1 has internal linkage
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  ```
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  — *end example*]
106
 
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- [*Note 1*:
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  These constraints do not apply to type names introduced by `typedef`
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  declarations and *alias-declaration*s.
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  [*Example 3*:
@@ -119,13 +119,13 @@ export using T = S; // OK, exports name T denoting type S
119
 
120
  — *end example*]
121
 
122
  — *end note*]
123
 
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- A redeclaration of an exported declaration of an entity is implicitly
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- exported. An exported redeclaration of a non-exported declaration of an
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- entity is ill-formed.
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  [*Example 4*:
129
 
130
  ``` cpp
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  export module M;
@@ -135,19 +135,16 @@ export typedef S S; // OK, does not redeclare an entity
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  export struct S; // error: exported declaration follows non-exported declaration
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  ```
137
 
138
  — *end example*]
139
 
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- A name is *exported* by a module if it is introduced or redeclared by an
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- exported declaration in the purview of that module.
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-
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- [*Note 2*: Exported names have either external linkage or no linkage;
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- see [[basic.link]]. Namespace-scope names exported by a module are
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- visible to name lookup in any translation unit importing that module;
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- see [[basic.scope.namespace]]. Class and enumeration member names are
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- visible to name lookup in any context in which a definition of the type
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- is reachable. — *end note*]
149
 
150
  [*Example 5*:
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152
  Interface unit of \`M\`
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@@ -195,50 +192,24 @@ int main() {
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  }
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  ```
197
 
198
  — *end example*]
199
 
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- [*Note 3*:
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-
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- Redeclaring a name in an *export-declaration* cannot change the linkage
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- of the name [[basic.link]].
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-
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- [*Example 6*:
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-
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- Interface unit of \`M\`
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-
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- ``` cpp
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- export module M;
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- static int f(); // #1
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- export int f(); // error: #1 gives internal linkage
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- struct S; // #2
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- export struct S; // error: #2 gives module linkage
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- namespace {
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- namespace N {
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- extern int x; // #3
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- }
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- }
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- export int N::x; // error: #3 gives internal linkage
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- ```
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-
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- — *end example*]
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-
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- — *end note*]
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-
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  [*Note 4*:
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  Declarations in an exported *namespace-definition* or in an exported
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  *linkage-specification* [[dcl.link]] are exported and subject to the
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  rules of exported declarations.
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- [*Example 7*:
234
 
235
  ``` cpp
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  export module M;
 
237
  export namespace N {
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  int x; // OK
239
- static_assert(1 == 1); // error: does not declare a name
240
  }
241
  ```
242
 
243
  — *end example*]
244
 
 
1
  ## Export declaration <a id="module.interface">[[module.interface]]</a>
2
 
3
  ``` bnf
4
  export-declaration:
5
+ export name-declaration
6
  export '{' declaration-seqₒₚₜ '}'
7
  export-keyword module-import-declaration
8
  ```
9
 
10
+ An *export-declaration* shall inhabit a namespace scope and appear in
11
  the purview of a module interface unit. An *export-declaration* shall
12
  not appear directly or indirectly within an unnamed namespace or a
13
  *private-module-fragment*. An *export-declaration* has the declarative
14
+ effects of its *name-declaration*, *declaration-seq* (if any), or
15
+ *module-import-declaration*. The *name-declaration* of an
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+ *export-declaration* shall not declare a partial specialization
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+ [[temp.decls.general]]. The *declaration-seq* of an *export-declaration*
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+ shall not contain an *export-declaration* or
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+ *module-import-declaration*.
20
 
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+ [*Note 1*: An *export-declaration* does not establish a
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+ scope. — *end note*]
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+
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+ A declaration is *exported* if it is declared within an
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+ *export-declaration* and inhabits a namespace scope or it is
26
 
 
 
27
  - a *namespace-definition* that contains an exported declaration, or
28
  - a declaration within a header unit [[module.import]] that introduces
29
  at least one name.
30
 
31
+ If an exported declaration is not within a header unit, it shall not
32
+ declare a name with internal linkage.
 
33
 
34
  [*Example 1*:
35
 
36
  Source file \`"a.h"\`
37
 
 
44
  ``` cpp
45
  module;
46
  #include "a.h" // error: declaration of x is not in the
47
  // purview of a module interface unit
48
  export module M;
49
+ export namespace {} // error: namespace has internal linkage
 
 
 
50
  namespace {
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  export int a2; // error: export of name with internal linkage
52
  }
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  export static int b; // error: b explicitly declared static
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  export int f(); // OK
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  export namespace N { } // OK
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+ export using namespace N; // OK
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  ```
58
 
59
  — *end example*]
60
 
61
+ If an exported declaration is a *using-declaration* [[namespace.udecl]]
62
+ and is not within a header unit, all entities to which all of the
63
  *using-declarator*s ultimately refer (if any) shall have been introduced
64
  with a name having external linkage.
65
 
66
  [*Example 2*:
67
 
 
102
  export using N::h; // error: #1 has internal linkage
103
  ```
104
 
105
  — *end example*]
106
 
107
+ [*Note 2*:
108
 
109
  These constraints do not apply to type names introduced by `typedef`
110
  declarations and *alias-declaration*s.
111
 
112
  [*Example 3*:
 
119
 
120
  — *end example*]
121
 
122
  — *end note*]
123
 
124
+ A redeclaration of an entity X is implicitly exported if X was
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+ introduced by an exported declaration; otherwise it shall not be
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+ exported.
127
 
128
  [*Example 4*:
129
 
130
  ``` cpp
131
  export module M;
 
135
  export struct S; // error: exported declaration follows non-exported declaration
136
  ```
137
 
138
  — *end example*]
139
 
140
+ [*Note 3*: Names introduced by exported declarations have either
141
+ external linkage or no linkage; see [[basic.link]]. Namespace-scope
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+ declarations exported by a module can be found by name lookup in any
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+ translation unit importing that module [[basic.lookup]]. Class and
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+ enumeration member names can be found by name lookup in any context in
145
+ which a definition of the type is reachable. — *end note*]
 
 
 
146
 
147
  [*Example 5*:
148
 
149
  Interface unit of \`M\`
150
 
 
192
  }
193
  ```
194
 
195
  — *end example*]
196
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
197
  [*Note 4*:
198
 
199
  Declarations in an exported *namespace-definition* or in an exported
200
  *linkage-specification* [[dcl.link]] are exported and subject to the
201
  rules of exported declarations.
202
 
203
+ [*Example 6*:
204
 
205
  ``` cpp
206
  export module M;
207
+ int g;
208
  export namespace N {
209
  int x; // OK
210
+ using ::g; // error: ::g has module linkage
211
  }
212
  ```
213
 
214
  — *end example*]
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