std::ranges::views::single, std::ranges::single_view

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Semiregular wrapper
semiregular_box
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewistream_view
Adaptors
views::all_tviews::all common_viewviews::common join_viewviews::join split_viewviews::split	take_viewviews::take drop_viewviews::drop take_while_viewviews::take_while drop_while_viewviews::drop_while	transform_viewviews::transform reverse_viewviews::reverse filter_viewviews::filter ref_view	views::counted elements_viewviews::elements keys_viewviews::keys values_viewviews::values

 

Defined in header <ranges>
template< std::copy_constructible T >   requires std::is_object_v<T> class single_view : public ranges::view_interface<single_view<T>>	(1)	(since C++20)
namespace views {     inline constexpr /*unspecified*/ single = /*unspecified*/; }	(2)	(since C++20)

1) Produces a view that contains exactly one element of a specified value.

2) The expression views::single(E) is expression-equivalent to single_view{E} for any suitable subexpression E.

Typical implementations of single_view store a single member of type semiregular_box<T>. For description purposes, this member is hereinafter called value_.

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

Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

Member functions

(constructor)	constructs a single_view (public member function)
begin	returns a pointer to the element (public member function)
end	returns a pointer past the element (public member function)
size [static]	returns 1 (one) (public static member function)
data	returns a pointer to the element (public member function)

std::ranges::single_view::single_view

single_view() = default;	(1)
constexpr explicit single_view( const T& t );	(2)
constexpr explicit single_view( T&& t );	(3)
template< class... Args >   requires std::constructible_from<T, Args...> constexpr explicit single_view( std::in_place_t, Args&&... args );	(4)

Constructs a single_view.

1) Default initializes value_.

2) Initializes value_ with t.

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

4) Initializes value_ as if by value_{std::in_place, std::forward<Args>(args)...}.

std::ranges::single_view::begin

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

Equivalent to return data();.

std::ranges::single_view::end

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

Equivalent to return data() + 1;.

std::ranges::single_view::size

static constexpr std::size_t size() noexcept;

Equivalent to return 1;.

This is a static function. This 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;

Returns value_.operator->().

Example

Run this code

#include <iostream>
#include <ranges>
#include <string>
#include <tuple>
 
int main()
{
    std::ranges::single_view sv1{3.1415}; // uses (const T&) constructor
 
    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 = \"" << str << "\"\n";
    std::ranges::single_view sv2{std::move(str)}; // uses (T&&) constructor
    std::cout << "6) *sv2.data(): \"" << *sv2.data() << "\"\n"
              << "7)  str = \"" << str << "\"\n";
 
    std::ranges::single_view<std::tuple<int, double, std::string>>
        sv3{std::in_place, 42, 3.14, "😄"}; // uses (std::in_place_t, Args&&... args)
 
    std::cout << "8)  sv3 keeps 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 keeps a tuple: { 42, 3.14, 😄 }

See also

ranges::empty_viewviews::empty (C++20)	an empty view with no elements (class template) (variable template)
ranges::split_viewviews::split (C++20)	a view over the subranges obtained from splitting another view using a delimiter (class template) (range adaptor object)