If E is an array type with element type T, the number of elements in the identifier-list shall be equal to the number of elements of E. Each vi is the name of an lvalue that refers to the element i of the array and whose type is T; the referenced type is T. [ Note: The top-level cv-qualifiers of T are cv. — end note ] [ Example:
auto f() -> int(&)[2]; auto [ x, y ] = f(); auto& [ xr, yr ] = f();
— end example ]
Otherwise, if the qualified-id std::tuple_size<E> names a complete type, the expression std::tuple_size<E>::value shall be a well-formed integral constant expression and the number of elements in the identifier-list shall be equal to the value of that expression. The unqualified-id get is looked up in the scope of E by class member access lookup, and if that finds at least one declaration, the initializer is e.get<i>(). Otherwise, the initializer is get<i>(e), where get is looked up in the associated namespaces. In either case, get<i> is interpreted as a template-id. [ Note: Ordinary unqualified lookup is not performed. — end note ] In either case, e is an lvalue if the type of the entity e is an lvalue reference and an xvalue otherwise. Given the type Ti designated by std::tuple_element<i, E>::type, each vi is a variable of type “reference to Ti” initialized with the initializer, where the reference is an lvalue reference if the initializer is an lvalue and an rvalue reference otherwise; the referenced type is Ti.
Otherwise, all of E's non-static data members shall be public direct members of E or of the same unambiguous public base class of E, E shall not have an anonymous union member, and the number of elements in the identifier-list shall be equal to the number of non-static data members of E. Designating the non-static data members of E as m0, m1, m2, ... (in declaration order), each vi is the name of an lvalue that refers to the member mi of e and whose type is cv Ti, where Ti is the declared type of that member; the referenced type is cv Ti. The lvalue is a bit-field if that member is a bit-field. [ Example:
struct S { int x1 : 2; volatile double y1; };
S f();
const auto [ x, y ] = f();
The type of the id-expression x is “const int”, the type of the id-expression y is “const volatile double”. — end example ]
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