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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General 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)

Concurrency support library (C++11)

Execution support library (C++26)

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 std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

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	constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

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 concat_viewviews::concat (C++26)(C++26)	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 closure objects range_adaptor_closure (C++23)

Range adaptor objects

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

repeat_view::begin

repeat_view::end

repeat_view::size

Deduction guides

Iterator

Member functions

repeat_view::iterator::iterator

repeat_view::iterator::operator*

repeat_view::iterator::operator[]

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

repeat_view::iterator::operator-- repeat_view::iterator::operator--(int)

repeat_view::iterator::operator+=

repeat_view::iterator::operator-=

Non-member functions

operator==(repeat_view::iterator) operator<=>(repeat_view::iterator)

operator+(repeat_view::iterator)

operator-(repeat_view::iterator)

 

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>> &&              (/*integer-like-with-usable-difference-type*/<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)
Helper concepts
concept /*integer-like-with-usable-difference-type*/ =     /*is-signed-integer-like*/<T> ||     (/*is-integer-like*/ <T> && std::weakly_incrementable<T>)	(3)	(exposition only*)

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<std::decay_t<decltype((E))>>(e) and repeat_view(e, f) respectively for any suitable subexpressions e and f.

3) Determines whether a type is integer-like and has a usable difference type.

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

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

Member	Definition
movable-box <W> value_	the repeating element of the view (exposition-only member object*)
Bound bound_	the sentinel value (exposition-only member object*)

Member functions

(constructor)	creates a repeat_view (public member function)
begin	obtains the beginning iterator of a repeat_view (public member function)
end	obtains the sentinel denoting the end of a repeat_view (public member function)
size	obtains the size of a repeat_view if it is sized (public member function)
Inherited from std::ranges::view_interface
empty	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	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	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back	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[]	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) Default-initializes value_ and value-initializes bound_ .

2) Initializes value_ with value and initializes bound_ with bound.

If Bound is not std::unreachable_sentinel_t and bool(bound >= 0) is false, the behavior is undefined.

3) Initializes value_ with std::move(value) and initializes bound_ with bound.

If Bound is not std::unreachable_sentinel_t and bool(bound >= 0) is false, the behavior is undefined.

4) Initializes value_ with std::make_from_tuple<T>(std::move(value_args)) and bound_ with std::make_from_tuple<Bound>(std::move(bound_args)).

If Bound is not std::unreachable_sentinel_t and bool(bound >= 0) is false, the behavior is undefined.

Parameters

value	-	the value to be repeatedly produced
bound	-	the bound
value_args	-	the tuple containing the initializers of value_
bound_args	-	the tuple containing the initializers of bound_

std::ranges::repeat_view::begin

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

Returns iterator (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 iterator (std::addressof(*value_ ), value_ ).

2) Returns 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 to-unsigned-like (bound_ ).

Deduction guides

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

Nested classes

iterator

the iterator type (exposition-only member class*)

Notes

Feature-test macro	Value	Std	Feature
__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 ...

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 4053	C++20	unary calls to views::repeat did not decay the argument	decay the argument
LWG 4054	C++20	calling views::repeat with a repeat_view did not create a nested repeat_view	creates a nested repeat_view

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)