variant (variadic)

For C++11 and above.

STL equivalent:- std::variant

template <typename... TTypes>

class variant

A variadic class that can contain one a several specified types in a type safe manner.

C++11 and C++14 support up to 32 types for visitor callback callbacks.

C++17 and above supports any number of visitor callback types.

Accepts functors, etl::overload and etl::visitor types as visitor callbacks.

Accepts etl::visit

20.28.0

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Error exception types

class variant_exception : public exception

class variant_incorrect_type_exception : public variant_exception

The error types emitted when a non-supported type is requested from the variant.

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Construction

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ETL_CONSTEXPR14 variant()

Default constructor.

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template <typename T>

ETL_CONSTEXPR14 variant(T&& value)

Constructor from a value.

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template <typename T, typename... TArgs>

ETL_CONSTEXPR14 explicit variant(etl::in_place_type_t<T>, TArgs&&... args)

Construct T from arguments.

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template <size_t Index, typename... TArgs>

ETL_CONSTEXPR14 explicit variant(etl::in_place_index_t<Index>, TArgs&&... args)

Construct from Index using args.

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template <typename T, typename U, typename... TArgs>

ETL_CONSTEXPR14 explicit variant(etl::in_place_type_t<T>,

std::initializer_list<U> init,

TArgs&&... args)

Construct from type, initializer_list and arguments.

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template <size_t Index, typename U, typename... TArgs>

ETL_CONSTEXPR14 explicit variant(etl::in_place_index_t<Index>,

std::initializer_list<U> init,

TArgs&&... args)

Construct from Index, initializer_list and arguments.

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ETL_CONSTEXPR14 variant(const variant& other)

Copy constructor.

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ETL_CONSTEXPR14 variant(variant&& other)

Move constructor.

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Operations

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template <typename T, typename... TArgs>

T& emplace(TArgs&&... args)

Set to type T using the construction parameters args.

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template <typename T>

variant& operator =(T&& value)

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variant& operator =(const variant& other)

Copies other to the current variant.

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variant& operator =(variant&& other)

Moves other to the current variant.

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constexpr bool valueless_by_exception() const noexcept

Returns true if the type id is etl::variant_npos.

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constexpr size_t index() const noexcept

Returns the index of the type contained in the variant.

Returns etl::variant_npos if the variant does not hold a valid type.

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void swap(variant& rhs) noexcept

Swaps rhs with the current variant.

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Access

Non-member functions

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get

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 etl::variant_alternative_t<Index, etl::variant<TTypes...>>&

get(etl::variant<TTypes...>& v)

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 etl::variant_alternative_t<Index, etl::variant<TTypes...>>&&

get(etl::variant<TTypes...>&& v)

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 const etl::variant_alternative_t<Index, const etl::variant<TTypes...>>&

get(const etl::variant<TTypes...>& v)

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 const etl::variant_alternative_t<Index, const etl::variant<TTypes...>>&&

get(const etl::variant<TTypes...>&& v)

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template <typenameT, typename... TTypes>

ETL_CONSTEXPR14 T& get(etl::variant<TTypes...>& v)

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template <typenameT, typename... TTypes>

ETL_CONSTEXPR14 T&& get(etl::variant<TTypes...>&& v)

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template <typenameT, typename... TTypes>

ETL_CONSTEXPR14 const T& get(const etl::variant<TTypes...>& v)

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template <typenameT, typename... TTypes>

ETL_CONSTEXPR14 const T&& get(const etl::variant<TTypes...>&& v)

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get_if

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 etl::add_pointer_t<etl::variant_alternative_t<Index, etl::variant<TTypes...>>>

get_if(etl::variant<TTypes...>* pv) noexcept

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 etl::add_pointer_t<const etl::variant_alternative_t<Index, etl::variant<TTypes...>>>

get_if(const etl::variant<TTypes...>* pv) noexcept

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template <typename T, typename... TTypes>

ETL_CONSTEXPR14 etl::add_pointer_t<T> get_if(etl::variant<TTypes...>* pv) noexcept

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template <typename T, typename... TTypes>

ETL_CONSTEXPR14 etl::add_pointer_t<const T> get_if(const etl::variant<TTypes...>* pv) noexcept

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Other

struct monostate

A default constructible type.

For use as the first state to turn a non-default constructible variant into a default constructible variant.

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template <typename... TTypes>

void swap(etl::variant<TTypes...>& lhs, etl::variant<TTypes...>& rhs)

Swaps lhs and rhs.

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template <typename... TTypes>

struct variant_size<etl::variant<TTypes...>>

The member constant value contains the number of types.

For C++17 and above.

template <typename... TTypes>

inline constexpr size_t variant_size_v = variant_size<TTypes...>::value;

Has the value equal to the number of types.

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Tests

Non-member functions

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template <typename T, typename... TTypes>

ETL_CONSTEXPR14 bool holds_alternative(const etl::variant<TTypes...>& v) noexcept

Checks if the variant v holds the alternative T.

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template <size_t Index, typename... TTypes>

ETL_CONSTEXPR14 bool holds_alternative(const etl::variant<TTypes...>& v) noexcept

Checks if the variant v holds the alternative Index.

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template <typename... TTypes>

ETL_CONSTEXPR14 bool holds_alternative(size_t index, const etl::variant<TTypes...>& v) noexcept

Checks if the variant v holds the alternative index.

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Visitation

For etl::visitor

For C++11 and C++14 the maximum number of visitor types is 32.

Code size may be minimised if one of the following macros are defined.

ETL_VARIANT_CPP11_MAX_8_TYPES

ETL_VARIANT_CPP11_MAX_16_TYPES

ETL_VARIANT_CPP11_MAX_24_TYPES

C++17 and above support any number of visitor callback types.

etl::variant provides member functions that support two methods of visitation.

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void accept_visitor(etl::visitor<TTypes...>& v)

Accepts an etl::visitor derived type.

See visitor

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template <typename TVisitor>

void accept_functor(TVisitor& v)

Accepts a functor that overrides operator() for each type.

See overload

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Visitation

For STL style etl::visit

20.28.0

The ETL implements an STL style visit function.

variant.h