variant (legacy)

A class that can contain one a several specified types in a type safe manner.
Supports up to eight types.
Supplies a nested reader visitor class that allows type safe access via sets of overloaded virtual read functions for each type.

Accepts etl::visit since 20.28.0.

If ETL_USE_LEGACY_VARIANT is defined then etl::variant is in the etl namespace.
If ETL_USE_LEGACY_VARIANT is not defined then etl::variant is in the etl::legacy namespace.
Since: 20.30.0.

Constructors

variant()

Description
Default constructor.

template <typename T>
variant(T value)

Description
Construct from value.
A static assert will occur if T is not a supported type.

Operations

template <typename T>
variant& operator =(typename parameter_type<T>::type value)

Description
Assigns a value.
A static assert occurs if the type T is not supported.

If C++11 is not supported

template <typename T, typename TP1>
T& emplace(const TP1& value1)

template <typename T, typename TP1, typename TP2>
T& emplace(const TP1& value1, const TP2& value2)

template <typename T, typename TP1, typename TP2, typename TP3>
T& emplace(const TP1& value1, const TP2& value2, const TP3& value3)

template <typename T, typename TP1, typename TP2, typename TP3, typename TP4>
T& emplace(const TP1& value1, const TP2& value2, const TP3& value3, const TP4& value4)

Description
Construct a T from multiple arguments.

If C++11 or greater is supported

template <typename T, typename... Args>
T& emplace(Args&&... args)

Description
Construct a Ts in-place using the supplied parameters.

void clear()

Description
Clears the variant of holding any type.

Access

template <typename T>
T& get()

Gets a value.
If T is a type not supported by the variant then a static assert occurs.
If T is a type that is not the type currently stored then a variant_incorrect_type_exception() error is raised.
If asserts or exceptions are not enabled then undefined behaviour occurs.

const template <typename T>
T& get() const

Gets a value.
If T is a type not supported by the variant then a static assert occurs.
If T is a type that is not the type currently stored then a variant_incorrect_type_exception() error is raised.
If asserts or exceptions are not enabled then undefined behaviour occurs.

T* upcast_ptr<T>()
const T* upcast_ptr<T>() const

For variant types that are polymorphic.
Up-casts the variant to type T*.
Types that cannot be up-cast will result in a nullptr return.
Since: 20.30.0

T& upcast<T>()
const T& upcast<T>() const

For variant types that are polymorphic.
Up-casts the variant to type T.
Types that cannot be up-cast will result in a runtime error etl::variant_not_a_base.
Since: 20.30.0

bool is_base_of<T>() const

Tests if the type T is a base of the current variant type.
Since: 20.30.0

call(reader& r)

Calls the appropriate overloaded r.read() function with the value.

template <typename T>
variant& operator =(typename parameter_type<T>::type value)

Assigns a value.
A static assert occurs if the type T is not supported.

Any value stored in the variant can be implicitly cast to its current type.
If the implicit cast is to a type not supported by the variant then a static assert occurs.
If the implicit cast is to a type that is not the type currently stored then a etl::variant_incorrect_type_exception error is raised.

Tests

template <typename T>
static bool is_supported_type()

Returns true if T is supported by the variant, otherwise false.

bool is_same_type(const variant& other) const

Returns true if the variant holds the same type as the other, otherwise false.

bool is_valid() const

Returns true if the variant holds a valid value, otherwise false.

template <typename T>
bool is_type() const

Returns true if T is the type currently stored in the variant, otherwise false.

Visitation

For STL style etl::visit 20.28.0

The ETL implements an STL style visit function.