etl/docs/types/tuple.md

title
tuple

{{< callout type="info">}} Header: tuple.h
From: 20.41.0
Similar to: std::tuple {{< /callout >}}

A fixed-size collection of heterogeneous values.

Adds additional functionality to std::tuple.

etl::tuple<typename... Types>

Template deduction guides

C++17 and above.

Template deduction guide from variadic arguments.

template <typename... TArgs>
tuple(TArgs... args) -> tuple<TArgs...>;

Template deduction guide from pair.

template <typename T1, typename T2>
tuple(ETL_OR_STD::pair<T1, T2>) -> tuple<T1, T2>;

Example

etl::tuple tp(1, 2.2, 3, std::string("4"));

Equivalent to:

etl::tuple<int, double, int, std::string> t(1, 2.2, 3, std::string("4"));

Make tuple

template <typename... Types>
ETL_NODISCARD
ETL_CONSTEXPR14
etl::tuple<etl::unwrap_ref_decay_t<Types>...> make_tuple(Types&&... args)

Example

auto t = etl::make_tuple(1, 2.2, 3, std::string("4"));

Equivalent to:

etl::tuple<int, double, int, std::string> t(1, 2.2, 3, std::string("4"));

---

Member types

value_type
  The first type contained by this tuple.
this_type
  The type of this tuple.
base_type
  The type of the base tuple to this tuple. This is a tuple of all types except for the first.
index_sequence_type
  The index_sequence type for this tuple.

Constructor

Default or copy constructs each element.
Can be initialised like a C array.

etl::array<int, 10> data = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

Access

template <size_t Index, typename Tuple>
etl::tuple_element;

Capacity

template <typename Tuple>
struct tuple_size;

ETL Extensions

template <typename T>
struct is_tuple

If T is a tuple then etl::is_tuple is defined as etl::true_type, otherwise etl::false_type.

Specialisations of STL to allow the use of C++ structured bindings.

template <typename... Types>
struct tuple_size<etl::tuple<Types...>>

Specialisation of tuple_size to allow the use of C++ structured bindings.
Declared in namespace std.

template <size_t Index, typename... Types>
struct tuple_element<Index, etl::tuple<Types...>>

Specialisation of tuple_element to allow the use of C++ structured bindings.
Declared in namespace std.

Convert an etl::tuple to a std::tuple

template <typename... Types>
ETL_NODISCARD
ETL_CONSTEXPR14
auto to_std(const etl::tuple<Types...>& etl_tuple)

Converts an etl::tuple to a std::tuple.
Enabled when STL is available.

---

template <typename... Types>
ETL_NODISCARD
ETL_CONSTEXPR14
auto to_std(etl::tuple<Types...>&& etl_tuple)

Converts an etl::tuple to a std::tuple.
Enabled when STL is available.

Convert an std::tuple to a etl::tuple

template <typename... Types>
ETL_NODISCARD
ETL_CONSTEXPR14
auto to_etl(const std::tuple<Types...>& std_tuple)

Converts a std::tuple to an etl::tuple.
Enabled when STL is available.

---

template <typename... Types>
ETL_NODISCARD
ETL_CONSTEXPR14
auto to_etl(std::tuple<Types...>&& std_tuple)

Converts a std::tuple to an etl::tuple.
Enabled when STL is available.

Create a tuple from selected elements of another

template <typename Tuple, size_t... Indices>
ETL_NODISCARD
ETL_CONSTEXPR14
auto select_from_tuple(Tuple&& tuple, etl::index_sequence<Indices...>)

Creates a new tuple by selecting elements from another, given a run time index sequence.
Static asserts if the number of indices does not match the tuple size.

---

template <size_t... Indices, typename Tuple>
ETL_NODISCARD
ETL_CONSTEXPR14
auto select_from_tuple(Tuple&& tuple)

Creates a new tuple by selecting elements from another, given a template parameter index sequence.
Static asserts if the number of indices does not match the tuple size.

Non-member functions

template <size_t Index, typename... Types>
ETL_CONSTEXPR14
etl::tuple_element_t<Index, etl::tuple<Types...>>& get(tuple<Types...>&);

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template <size_t Index, typename... Types>
ETL_CONSTEXPR14 
etl::tuple_element_t<Index, etl::tuple<Types...>>&& get(tuple<Types...>&&);

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template <size_t Index, typename... Types>
ETL_CONSTEXPR14 
const etl::tuple_element_t<Index, etl::tuple<Types...>>& get(const tuple<Types...>&);

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template <size_t Index, typename... Types>
ETL_CONSTEXPR14 
const etl::tuple_element_t<Index, etl::tuple<Types...>>&& get(const tuple<Types...>&&);

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template <typename T, typename... Types>
ETL_CONSTEXPR14
T& get(tuple<Types...>&);

---

template <typename T, typename... Types>
ETL_CONSTEXPR14
T&& get(tuple<Types...>&&);

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template <typename T, typename... Types>
ETL_CONSTEXPR14
const T& get(const tuple<Types...>&);

---

template <typename T, typename... Types>
ETL_CONSTEXPR14
const T&& get(const tuple<Types...>&&);

---

template <typename TFunction, typename TTuple>
ETL_CONSTEXPR14
auto apply(TFunction&& f, TTuple&& t);

Invokes the callable object f (via etl::invoke) with the elements of the tuple t expanded as its arguments. Equivalent to std::apply.

int add(int a, int b, int c) { return a + b + c; }

auto t = etl::make_tuple(1, 2, 3);
int sum = etl::apply(add, t); // sum == 6