std::ranges::views::repeat, std::ranges::repeat_view - cppreference.com (original) (raw)

Defined in header
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)
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)

  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.

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

Contents

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.

[edit] 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*)

[edit] 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) [edit]
cbegin(C++23) returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface) [edit]
cend(C++23) returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface) [edit]
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) [edit]
front returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface) [edit]
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) [edit]
operator[] returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface) [edit]

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](repeat%5Fview.html#value)_ and value-initializes _[bound](repeat%5Fview.html#bound)_ .

  2. Initializes _[value](repeat%5Fview.html#value)_ with value and initializes _[bound](repeat%5Fview.html#bound)_ with bound.

  3. Initializes _[value](repeat%5Fview.html#value)_ with std::move(value) and initializes _[bound](repeat%5Fview.html#bound)_ with bound.

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::end

[edit] Deduction guides

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

[edit] Nested classes

| | the iterator type(exposition-only member class*) | | ---------------------------------------------------- |

[edit] Notes

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

[edit] Example

#include #include #include 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 ...

[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 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_viewdid not create a nested repeat_view creates a nestedrepeat_view

[edit] See also