21 Language support library [language.support]

21.9 Initializer lists [support.initlist]

The header <initializer_list> defines a class template and several support functions related to list-initialization (see [dcl.init.list]).

All functions specified in this subclause are signal-safe ([csignal.syn]).

21.9.1 Header <initializer_list> synopsis [initializer_list.syn]

namespace std {
  template<class E> class initializer_list {
  public:
    using value_type      = E;
    using reference       = const E&;
    using const_reference = const E&;
    using size_type       = size_t;

    using iterator        = const E*;
    using const_iterator  = const E*;

    constexpr initializer_list() noexcept;

    constexpr size_t size() const noexcept;     // number of elements
    constexpr const E* begin() const noexcept;  // first element
    constexpr const E* end() const noexcept;    // one past the last element
  };

  // [support.initlist.range], initializer list range access
  template<class E> constexpr const E* begin(initializer_list<E> il) noexcept;
  template<class E> constexpr const E* end(initializer_list<E> il) noexcept;
}

An object of type initializer_list<E> provides access to an array of objects of type const E.

[ Note

A pair of pointers or a pointer plus a length would be obvious representations for initializer_list.

initializer_list is used to implement initializer lists as specified in [dcl.init.list].

Copying an initializer list does not copy the underlying elements.

— end note

]

If an explicit specialization or partial specialization of initializer_list is declared, the program is ill-formed.

21.9.2 Initializer list constructors [support.initlist.cons]

constexpr initializer_list() noexcept;

Effects: Constructs an empty initializer_list object.

Postconditions: size() == 0.

21.9.3 Initializer list access [support.initlist.access]

constexpr const E* begin() const noexcept;

Returns: A pointer to the beginning of the array.

If size() == 0 the values of begin() and end() are unspecified but they shall be identical.

constexpr const E* end() const noexcept;

Returns: begin() + size().

constexpr size_t size() const noexcept;

Returns: The number of elements in the array.

Complexity: Constant time.

21.9.4 Initializer list range access [support.initlist.range]

template<class E> constexpr const E* begin(initializer_list<E> il) noexcept;

Returns: il.begin().

template<class E> constexpr const E* end(initializer_list<E> il) noexcept;