9 Declarations [dcl.dcl]

9.3 Declarators [dcl.decl]

9.3.1 General [dcl.decl.general]

A declarator declares a single variable, function, or type, within a declaration.
The init-declarator-list appearing in a simple-declaration is a comma-separated sequence of declarators, each of which can have an initializer.
In all contexts, a declarator is interpreted as given below.
Where an abstract-declarator can be used (or omitted) in place of a declarator ([dcl.fct], [except.pre]), it is as if a unique identifier were included in the appropriate place ([dcl.name]).
The preceding specifiers indicate the type, storage duration, linkage, or other properties of the entity or entities being declared.
Each declarator specifies one entity and (optionally) names it and/or modifies the type of the specifiers with operators such as * (pointer to) and () (function returning).
[Note 1: 
An init-declarator can also specify an initializer ([dcl.init]).
— end note]
Each init-declarator or member-declarator in a declaration is analyzed separately as if it were in a declaration by itself.
[Note 2: 
A declaration with several declarators is usually equivalent to the corresponding sequence of declarations each with a single declarator.
That is, T D1, D2, ... Dn; is usually equivalent to T D1; T D2; ... T Dn; where T is a decl-specifier-seq and each Di is an init-declarator or member-declarator.
One exception is when a name introduced by one of the declarators hides a type name used by the decl-specifiers, so that when the same decl-specifiers are used in a subsequent declaration, they do not have the same meaning, as in struct S { /* ... */ }; S S, T; // declare two instances of struct S which is not equivalent to struct S { /* ... */ }; S S; S T; // error
Another exception is when T is auto ([dcl.spec.auto]), for example: auto i = 1, j = 2.0; // error: deduced types for i and j do not match as opposed to auto i = 1; // OK, i deduced to have type int auto j = 2.0; // OK, j deduced to have type double
— end note]
The optional requires-clause in an init-declarator or member-declarator shall be present only if the declarator declares a templated function ([temp.pre]).
When present after a declarator, the requires-clause is called the trailing requires-clause.
The trailing requires-clause introduces the constraint-expression that results from interpreting its constraint-logical-or-expression as a constraint-expression.
[Example 1: void f1(int a) requires true; // error: non-templated function template<typename T> auto f2(T a) -> bool requires true; // OK template<typename T> auto f3(T a) requires true -> bool; // error: requires-clause precedes trailing-return-type void (*pf)() requires true; // error: constraint on a variable void g(int (*)() requires true); // error: constraint on a parameter-declaration auto* p = new void(*)(char) requires true; // error: not a function declaration — end example]