variant Class

Article
08/03/2021

Any instance of variant at any given time either holds a value of one of its alternative types, or it holds no value.

Syntax

template <class... Types>
    class variant

Members

Constructors

Name	Description
variant	Constructs an object of type `variant`.

Functions

Name	Description
emplace	Creates a new contained value.
index	Returns the index of a contained value.
swap
valueless_by_exception	Returns `false` if the variant holds a value.

Operators

Name	Description
operator=	Replaces the variant with a copy of another variant.

emplace

Creates a new contained value.

template <class T, class... Args>
    T& emplace(Args&&...);
template <class T, class U, class... Args>
    T& emplace(initializer_list<U>, Args&&...);
template <size_t I, class... Args>
    variant_alternative_t<I, variant<Types...>>& emplace(Args&&...);
template <size_t I, class U, class... Args>
    variant_alternative_t<I, variant<Types...>>& emplace(initializer_list<U>, Args&&...);

index

Returns the index of a contained value.

constexpr size_t index() const noexcept;

variant

Constructs an object of type variant. Also includes a destructor.

constexpr variant() noexcept(see below);
variant(const variant&);
variant(variant&&) noexcept(see below);
template <class T>
    constexpr variant(T&&) noexcept(see below);
template <class T, class... Args>
    constexpr explicit variant(in_place_type_t<T>, Args&&...);
template <class T, class U, class... Args>
    constexpr explicit variant(in_place_type_t<T>, initializer_list<U>, Args&&...);
template <size_t I, class... Args>
    constexpr explicit variant(in_place_index_t<I>, Args&&...);
template <size_t I, class U, class... Args>
    constexpr explicit variant(in_place_index_t<I>, initializer_list<U>, Args&&...);

template <class Alloc>
    variant(allocator_arg_t, const Al&);
template <class Alloc>
    variant(allocator_arg_t, const Al&, const variant&);
template <class Alloc>
    variant(allocator_arg_t, const Al&, variant&&);
template <class Alloc, class T>
    variant(allocator_arg_t, const Al&, T&&);
template <class Alloc, class T, class... Args>
    variant(allocator_arg_t, const Al&, in_place_type_t<T>, Args&&...);
template <class Alloc, class T, class U, class... Args>
    variant(allocator_arg_t, const Al&, in_place_type_t<T>, initializer_list<U>, Args&&...);
template <class Alloc, size_t I, class... Args>
    variant(allocator_arg_t, const Al&, in_place_index_t<I>, Args&&...);
template <class Alloc, size_t I, class U, class... Args>
    variant(allocator_arg_t, const Al&, in_place_index_t<I>, initializer_list<U>, Args&&...);

~variant();

Parameters

Al
The allocator class to use with this object.

operator=

Replaces the variant with a copy of another variant.

variant& operator=(const variant&);
variant& operator=(variant&&) noexcept(see below);
template <class T>
    variant& operator=(T&&) noexcept(see below);

swap

void swap(variant&) noexcept(see below);

valueless_by_exception

Returns false if the variant holds a value.

constexpr bool valueless_by_exception() const noexcept;

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