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[basic.def]

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  ## Declarations and definitions <a id="basic.def">[[basic.def]]</a>
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- A declaration (Clause  [[dcl.dcl]]) may introduce one or more names into
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- a translation unit or redeclare names introduced by previous
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- declarations. If so, the declaration specifies the interpretation and
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- attributes of these names. A declaration may also have effects
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  including:
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- - a static assertion (Clause  [[dcl.dcl]]),
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- - controlling template instantiation ([[temp.explicit]]),
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- - guiding template argument deduction for constructors (
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- [[temp.deduct.guide]]),
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- - use of attributes (Clause  [[dcl.dcl]]), and
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  - nothing (in the case of an *empty-declaration*).
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- A declaration is a *definition* unless
 
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- - it declares a function without specifying the function’s body (
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- [[dcl.fct.def]]),
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- - it contains the `extern` specifier ([[dcl.stc]]) or a
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- *linkage-specification*[^1] ([[dcl.link]]) and neither an
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- *initializer* nor a *function-body*,
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- - it declares a non-inline static data member in a class definition (
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- [[class.mem]],  [[class.static]]),
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  - it declares a static data member outside a class definition and the
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  variable was defined within the class with the `constexpr` specifier
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- (this usage is deprecated; see [[depr.static_constexpr]]),
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- - it is a class name declaration ([[class.name]]),
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- - it is an *opaque-enum-declaration* ([[dcl.enum]]),
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- - it is a *template-parameter* ([[temp.param]]),
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- - it is a *parameter-declaration* ([[dcl.fct]]) in a function
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- declarator that is not the *declarator* of a *function-definition*,
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- - it is a `typedef` declaration ([[dcl.typedef]]),
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- - it is an *alias-declaration* ([[dcl.typedef]]),
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- - it is a *using-declaration* ([[namespace.udecl]]),
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- - it is a *deduction-guide* ([[temp.deduct.guide]]),
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- - it is a *static_assert-declaration* (Clause  [[dcl.dcl]]),
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- - it is an *attribute-declaration* (Clause  [[dcl.dcl]]),
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- - it is an *empty-declaration* (Clause  [[dcl.dcl]]),
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- - it is a *using-directive* ([[namespace.udir]]),
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- - it is an explicit instantiation declaration ([[temp.explicit]]), or
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- - it is an explicit specialization ([[temp.expl.spec]]) whose
 
 
 
 
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  *declaration* is not a definition.
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  [*Example 1*:
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  All but one of the following are definitions:
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  ``` cpp
@@ -75,25 +83,25 @@ extern X anotherX; // declares anotherX
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  using N::d; // declares d
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  ```
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  — *end example*]
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- [*Note 1*: In some circumstances, C++implementations implicitly define
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- the default constructor ([[class.ctor]]), copy constructor (
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- [[class.copy]]), move constructor ([[class.copy]]), copy assignment
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- operator ([[class.copy]]), move assignment operator ([[class.copy]]),
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- or destructor ([[class.dtor]]) member functions. — *end note*]
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  [*Example 2*:
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  Given
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  ``` cpp
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  #include <string>
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  struct C {
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- std::string s; // std::string is the standard library class (Clause~[strings])
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  };
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  int main() {
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  C a;
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  C b = a;
@@ -119,10 +127,11 @@ struct C {
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  ```
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  — *end example*]
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  [*Note 2*: A class name can also be implicitly declared by an
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- *elaborated-type-specifier* ([[dcl.type.elab]]). — *end note*]
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- A program is ill-formed if the definition of any object gives the object
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- an incomplete type ([[basic.types]]).
 
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  ## Declarations and definitions <a id="basic.def">[[basic.def]]</a>
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+ A declaration [[dcl.dcl]] may introduce one or more names into a
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+ translation unit or redeclare names introduced by previous declarations.
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+ If so, the declaration specifies the interpretation and semantic
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+ properties of these names. A declaration may also have effects
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  including:
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+ - a static assertion [[dcl.pre]],
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+ - controlling template instantiation [[temp.explicit]],
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+ - guiding template argument deduction for constructors
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+ [[temp.deduct.guide]],
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+ - use of attributes [[dcl.attr]], and
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  - nothing (in the case of an *empty-declaration*).
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+ Each entity declared by a *declaration* is also *defined* by that
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+ declaration unless:
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+ - it declares a function without specifying the function’s body
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+ [[dcl.fct.def]],
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+ - it contains the `extern` specifier [[dcl.stc]] or a
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+ *linkage-specification*[^1] [[dcl.link]] and neither an *initializer*
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+ nor a *function-body*,
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+ - it declares a non-inline static data member in a class definition (
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+ [[class.mem]], [[class.static]]),
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  - it declares a static data member outside a class definition and the
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  variable was defined within the class with the `constexpr` specifier
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+ (this usage is deprecated; see [[depr.static.constexpr]]),
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+ - it is introduced by an *elaborated-type-specifier* [[class.name]],
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+ - it is an *opaque-enum-declaration* [[dcl.enum]],
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+ - it is a *template-parameter* [[temp.param]],
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+ - it is a *parameter-declaration* [[dcl.fct]] in a function declarator
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+ that is not the *declarator* of a *function-definition*,
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+ - it is a `typedef` declaration [[dcl.typedef]],
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+ - it is an *alias-declaration* [[dcl.typedef]],
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+ - it is a *using-declaration* [[namespace.udecl]],
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+ - it is a *deduction-guide* [[temp.deduct.guide]],
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+ - it is a *static_assert-declaration* [[dcl.pre]],
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+ - it is an *attribute-declaration* [[dcl.pre]],
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+ - it is an *empty-declaration* [[dcl.pre]],
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+ - it is a *using-directive* [[namespace.udir]],
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+ - it is a *using-enum-declaration* [[enum.udecl]],
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+ - it is a *template-declaration* [[temp.pre]] whose *template-head* is
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+ not followed by either a *concept-definition* or a *declaration* that
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+ defines a function, a class, a variable, or a static data member.
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+ - it is an explicit instantiation declaration [[temp.explicit]], or
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+ - it is an explicit specialization [[temp.expl.spec]] whose
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  *declaration* is not a definition.
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+ A declaration is said to be a *definition* of each entity that it
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+ defines.
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+
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  [*Example 1*:
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  All but one of the following are definitions:
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  ``` cpp
 
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  using N::d; // declares d
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  ```
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  — *end example*]
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+ [*Note 1*: In some circumstances, C++ implementations implicitly
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+ define the default constructor [[class.default.ctor]], copy constructor,
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+ move constructor [[class.copy.ctor]], copy assignment operator, move
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+ assignment operator [[class.copy.assign]], or destructor [[class.dtor]]
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+ member functions. — *end note*]
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  [*Example 2*:
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  Given
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  ``` cpp
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  #include <string>
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  struct C {
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+ std::string s; // std::string is the standard library class[string.classes]
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  };
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  int main() {
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  C a;
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  C b = a;
 
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  ```
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  — *end example*]
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  [*Note 2*: A class name can also be implicitly declared by an
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+ *elaborated-type-specifier* [[dcl.type.elab]]. — *end note*]
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+ In the definition of an object, the type of that object shall not be an
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+ incomplete type [[basic.types]], an abstract class type
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+ [[class.abstract]], or a (possibly multi-dimensional) array thereof.
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