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

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 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. See CustomizationPointObject for details.

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 only 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 only 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 only if it satisfies `bidirectional_range` and `common_range` (public member function of `std::ranges::view_interface<D>`)
operator[]	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>`)

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_ ), bound_ ).

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

#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`

ranges::iota_viewviews::iota (C++20)	a `view` consisting of a sequence generated by repeatedly incrementing an initial value (class template) (customization point object)
views::indices (C++26)	a `view` that generates a sequence of increasing values from `0` up to `n` (customization point object)

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

Customization point objects

Data members

Member functions

Inherited from `std::ranges::view_interface`

std::ranges::repeat_view::repeat_view

Parameters

std::ranges::repeat_view::begin

std::ranges::repeat_view::end

std::ranges::repeat_view::size

Deduction guides

Nested classes

Notes

Example

Defect reports

See also

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

Customization point objects

Data members

Member functions

Inherited from std::ranges::view_interface

std::ranges::repeat_view::repeat_view

Parameters

std::ranges::repeat_view::begin

std::ranges::repeat_view::end

std::ranges::repeat_view::size

Deduction guides

Nested classes

Notes

Example

Defect reports

See also

Inherited from `std::ranges::view_interface`