std::ranges::views::repeat, std::ranges::repeat_view

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Ranges library (C++20)

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Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_trange_value_trange_reference_t	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)	elements_of (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Range factories
empty_viewviews::empty single_viewviews::single	iota_viewviews::iota repeat_viewviews::repeat (C++23)(C++23)	basic_istream_viewviews::istream
Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23) filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23) lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)
Range generators
std::generator (C++23)
Range adaptor objects
Range adaptor closure objects
range_adaptor_closure (C++23)
Helper items
copyable-box movable-box (until C++23)(C++23)	simple-view non-propagating-cache

 

std::ranges::repeat_view

Member functions

repeat_view::repeat_view (C++23)

repeat_view::begin (C++23)

repeat_view::end (C++23)

repeat_view::size (C++23)

Deduction guides (C++23)

Iterator

Member functions

repeat_view::iterator::iterator (C++23)

repeat_view::iterator::operator* (C++23)

repeat_view::iterator::operator[] (C++23)

repeat_view::iterator::operator++ repeat_view::iterator::operator++(int) (C++23)(C++23)

repeat_view::iterator::operator-- repeat_view::iterator::operator--(int) (C++23)(C++23)

repeat_view::iterator::operator+= (C++23)

repeat_view::iterator::operator-= (C++23)

Non-member functions

operator==(repeat_view::iterator) operator<=>(repeat_view::iterator) (C++23)(C++23)

operator+(repeat_view::iterator) (C++23)

operator-(repeat_view::iterator) (C++23)

 

Defined in header <ranges>
template< std::move_constructible W,           std::semiregular Bound = std::unreachable_sentinel_t >     requires (std::is_object_v<W> && std::same_as<W, std::remove_cv_t<W>> &&              (/*is-integer-like*/<Bound> ||               std::same_as<Bound, std::unreachable_sentinel_t>)) class repeat_view : public ranges::view_interface<repeat_view<W, Bound>>	(1)	(since C++23)
namespace views {     inline constexpr /*unspecified*/ repeat = /*unspecified*/; }	(2)	(since C++23)
Call signature
template< class W >     requires /* see below */ constexpr /* see below */ repeat( W&& value );		(since C++23)
template< class W, class Bound >     requires /* see below */ constexpr /* see below */ repeat( W&& value, Bound&& bound );		(since C++23)

1) A range factory that generates a sequence of elements by repeatedly producing the same value. Can be either bounded or unbounded (infinite).

2) views::repeat(e) and views::repeat(e, f) are expression-equivalent to (has the same effect as) repeat_view(e) and repeat_view(e, f) respectively for any suitable subexpressions e and f.

Customization point objects

The name views::repeat denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __repeat_fn.

All instances of __repeat_fn are equal. The effects of invoking different instances of type __repeat_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, views::repeat can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to views::repeat above, __repeat_fn models

• std::invocable<__repeat_fn, Args...>,
• std::invocable<const __repeat_fn, Args...>,
• std::invocable<__repeat_fn&, Args...>, and
• std::invocable<const __repeat_fn&, Args...>.
  

Otherwise, no function call operator of __repeat_fn participates in overload resolution.

Data members

Typical implementation of repeat_view holds two non-static data members:

• value_ (exposition only*) - The beginning value of wrapped type /*movable-box*/<W>, and
• bound_ (exposition only*) - The sentinel value of type Bound.

Member functions

(constructor) (C++23)	creates a repeat_view (public member function)
begin (C++23)	obtains the beginning iterator of a repeat_view (public member function)
end (C++23)	obtains the sentinel denoting the end of a repeat_view (public member function)
size (C++23)	obtains the size of a repeat_view if it is sized (public member function)
Inherited from std::ranges::view_interface
empty (C++20)	returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function of std::ranges::view_interface<D>)
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
operator bool (C++20)	returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
front (C++20)	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back (C++20)	returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>)
operator[] (C++20)	returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

std::ranges::repeat_view::repeat_view

repeat_view() requires std::default_initializable<W> = default;	(1)	(since C++23)
constexpr explicit repeat_view( const W& value, Bound bound = Bound() );	(2)	(since C++23)
constexpr explicit repeat_view( W&& value, Bound bound = Bound() );	(3)	(since C++23)
template < class... WArgs, class... BoundArgs >   requires std::constructible_from<W, WArgs...>         && std::constructible_from<Bound, BoundArgs...> constexpr explicit repeat( std::piecewise_construct_t,                            std::tuple<WArgs...> value_args,                            std::tuple<BoundArgs...> bound_args = std::tuple<>{} );	(4)	(since C++23)

1) Value-initializes value_ and bound_ via their default member initializers (= W() and = Bound()).

2) Initializes value_ with value and initializes bound_ with bound. The behavior is undefined if Bound is not std::unreachable_sentinel_t and bool(bound >= 0) is false.

3) Initializes value_ with std::move(value) and initializes bound_ with bound. The behavior is undefined if Bound is not std::unreachable_sentinel_t and bool(bound >= 0) is false.

4) Initializes value_ and bound_ through piecewise construction.

Parameters

value	-	the value to be repeatedly produced
bound	-	the bound

std::ranges::repeat_view::begin

constexpr /*iterator*/ begin() const;		(since C++23)

Returns an iterator initialized with std::addressof(*value_).

std::ranges::repeat_view::end

constexpr /*iterator*/ end() const     requires (!std::same_as<Bound, std::unreachable_sentinel_t>);	(1)	(since C++23)
constexpr std::unreachable_sentinel_t end() const;	(2)	(since C++23)

1) Returns an iterator initialized with std::addressof(*value_) and bound_.

2) Returns an std::unreachable_sentinel.

std::ranges::repeat_view::size

constexpr auto size() const     requires (!std::same_as<Bound, std::unreachable_sentinel_t>);		(since C++23)

Returns the size of the view if the view is bounded. Equivalent to return /*to-unsigned-like*/(bound_);.

The exposition-only function template to-unsigned-like converts its argument (which must be integer-like) to the corresponding unsigned version of the argument type.

Deduction guides

template< class W, class Bound > repeat_view( W, Bound ) -> repeat_view<W, Bound>;		(since C++23)

Nested classes

iterator (C++23)

the iterator type (exposition-only member class*)

Notes

If Bound is not std::unreachable_sentinel_t, the repeat_view models sized_range and common_range.

Feature-test macro	Value	Std	Comment
__cpp_lib_ranges_repeat	202207L	(C++23)	std::ranges::repeat_view

Example

Run this code

#include <iostream>
#include <ranges>
#include <string_view>
using namespace std::literals;
 
int main()
{
    // bounded overload
    for (auto s: std::views::repeat("C++"sv, 3))
        std::cout << s << ' ';
    std::cout << '\n';
 
    // unbounded overload
    for (auto s : std::views::repeat("I know that you know that"sv)
                | std::views::take(3))
        std::cout << s << ' ';
    std::cout << "...\n";
}

Output:

C++ C++ C++
I know that you know that I know that you know that I know that you know that ...

See also

ranges::iota_viewviews::iota (C++20)

a view consisting of a sequence generated by repeatedly incrementing an initial value (class template) (customization point object)