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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../ranges/single_view.html below:

std::ranges::views::single, std::ranges::single_view - cppreference.com

1)

Produces a

view

that contains exactly one element of a specified value.

The lifetime of the element is bound to the parent single_view. Copying single_view makes a copy of the element.

Customization point objects

The name views::single denotes a customization point object, which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.

[edit] Data members Member Definition copyable-box <T> value_ (until C++23) the single element of the view
(exposition-only member object*) movable-box <T> value_ (since C++23) the single element of the view
(exposition-only member object*) [edit] Member functions constructs a single_view
(public member function) returns a pointer to the element
(public member function) returns a pointer past the element
(public member function) returns false
(public static member function) returns 1
(public static member function) returns a pointer to the element
(public member function) Inherited from std::ranges::view_interface returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit] returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit] returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit] returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit] returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range
(public member function of std::ranges::view_interface<D>) [edit] returns the n^th element in the derived view, provided only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit] std::ranges::single_view::single_view (1) (since C++20) (2)

constexpr explicit single_view( const T& t );

(since C++20)
(until C++23) (since C++23)

constexpr explicit single_view( T&& t );

(3) (since C++20) (4) (since C++20)

Constructs a single_view.

1) Default initializes value_, which value-initializes its contained value.

2) Initializes value_ with t.

3) Initializes value_ with std::move(t).

std::ranges::single_view::begin

constexpr T* begin() noexcept; constexpr const T* begin() const noexcept;

(since C++20)

Equivalent to return data();.

std::ranges::single_view::end

constexpr T* end() noexcept; constexpr const T* end() const noexcept;

(since C++20)

Equivalent to return data() + 1;.

std::ranges::single_view::empty

static constexpr bool empty() noexcept;

(since C++20)

Equivalent to return false;.

std::ranges::single_view::size (since C++20)

Equivalent to return 1;.

Makes single_view model /*tiny-range*/ as required by split_view.

std::ranges::single_view::data

constexpr T* data() noexcept; constexpr const T* data() const noexcept;

(since C++20)

Returns a pointer to the contained value of value_. The behavior is undefined if value_ does not contains a value.

[edit] Deduction guides

template< class T > single_view( T ) -> single_view<T>;

(since C++20) [edit] Notes

For a single_view, the inherited empty member function always returns false, and the inherited operator bool conversion function always returns true.

[edit] Example

#include <iomanip>
#include <iostream>
#include <ranges>
#include <string>
#include <tuple>
 
int main()
{
    constexpr std::ranges::single_view sv1{3.1415}; // uses (const T&) constructor
    static_assert(sv1);
    static_assert(not sv1.empty());
 
    std::cout << "1) *sv1.data(): " << *sv1.data() << '\n'
              << "2) *sv1.begin(): " << *sv1.begin() << '\n'
              << "3)  sv1.size(): " << sv1.size() << '\n'
              << "4)  distance: " << std::distance(sv1.begin(), sv1.end()) << '\n';
 
    std::string str{"C++20"};
    std::cout << "5)  str = " << std::quoted(str) << '\n';
    std::ranges::single_view sv2{std::move(str)}; // uses (T&&) constructor
    std::cout << "6) *sv2.data(): " << std::quoted(*sv2.data()) << '\n'
              << "7)  str = " << std::quoted(str) << '\n';
 
    std::ranges::single_view<std::tuple<int, double, std::string>>
        sv3{std::in_place, 42, 3.14, "ð"}; // uses (std::in_place_t, Args&&... args)
 
    std::cout << "8)  sv3 holds a tuple: { "
              << std::get<0>(sv3[0]) << ", "
              << std::get<1>(sv3[0]) << ", "
              << std::get<2>(sv3[0]) << " }\n";
}

Output:

1) *sv1.data(): 3.1415
2) *sv1.begin(): 3.1415
3)  sv1.size(): 1
4)  distance: 1
5)  str = "C++20"
6) *sv2.data(): "C++20"
7)  str = ""
8)  sv3 holds a tuple: { 42, 3.14, ð }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior LWG 3428 C++20 single_view was convertible from std::in_place_t the constructor is made explicit LWG 4035 C++20 single_view did not provide the member function empty() provides empty() P2367R0 C++20 deduction guides for single_view failed to decay the argument;
views::single copied but not wrapped a single_view a decaying guide provided;
made always wrapping [edit] See also

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