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      std::ranges::views::cache_latest,std::ranges::cache_latest_view

      From cppreference.com
      <cpp‎ |ranges
       
       
      Ranges library
      Range adaptors
       
      std::ranges::cache_latest_view
       
      Defined in header<ranges>
      template<ranges::input_range V>

          requiresranges::view<V>
      class cache_latest_view

         :publicranges::view_interface<cache_latest_view<V>>
      		 (1)(since C++26)
      namespace views{

         inlineconstexpr/* unspecified */ cache_latest=/* unspecified */;

      }
      		 (2)(since C++26)
      Call signature
      template<ranges::viewable_range R>

          requires/* see below */

      constexprranges::viewauto cache_latest( R&& r);
      		(since C++26)
      1) A range adaptor that caches the last-accessed element of its underlyingview so that the element does not have to be recomputed on repeated access.
      2)RangeAdaptorObject. The expressionviews::cache_latest(e) isexpression-equivalent tocache_latest_view(e) for any suitable subexpressione.

      cache_latest_view is aninput_range-only that never modelsborrowed_range orcommon_range.

      Contents

      [edit]Nested types

      Type Definition
      CacheT(private)std::conditional_t<std::is_reference_v<ranges::range_reference_t<V>>,
                         std::add_pointer_t<ranges::range_reference_t<V>>,
                         ranges::range_reference_t<V>>
      (exposition-only member type*)

      [edit]Data members

      Member Description
      Vbase_(private) the underlying view
      (exposition-only member object*)
      non-propagating-cache<CacheT>cache_(private) an object that caches the result of the last indirection of the current iterator
      (exposition-only member object*)

      [edit]Member functions

      constructs acache_latest_view
      (public member function)
      returns a copy of the underlying (adapted) view
      (public member function)
      returns an iterator to the beginning
      (public member function)
      returns an iterator or a sentinel to the end
      (public member function)
      returns the number of elements. Provided only if the underlying (adapted) range satisfiessized_range.
      (public member function)
      Inherited fromstd::ranges::view_interface
      returns whether the derived view is empty, provided only if it satisfiessized_range orforward_range
      (public member function ofstd::ranges::view_interface<D>)[edit]
      (C++23)
      		 returns a constant iterator to the beginning of the range
      (public member function ofstd::ranges::view_interface<D>)[edit]
      (C++23)
      		 returns a sentinel for the constant iterator of the range
      (public member function ofstd::ranges::view_interface<D>)[edit]
      returns whether the derived view is not empty, provided only ifranges::empty is applicable to it
      (public member function ofstd::ranges::view_interface<D>)[edit]
      gets the address of derived view's data, provided only if its iterator type satisfiescontiguous_iterator
      (public member function ofstd::ranges::view_interface<D>)[edit]
      returns the first element in the derived view, provided if it satisfiesforward_range
      (public member function ofstd::ranges::view_interface<D>)[edit]
      returns the last element in the derived view, provided only if it satisfiesbidirectional_range andcommon_range
      (public member function ofstd::ranges::view_interface<D>)[edit]
      returns thenth element in the derived view, provided only if it satisfiesrandom_access_range
      (public member function ofstd::ranges::view_interface<D>)[edit]

      std::ranges::cache_latest_view::cache_latest_view

      cache_latest_view() requiresstd::default_initializable<V>=default;
      		 (1)(since C++26)
      constexprexplicit cache_latest_view( V base);
      		 (2)(since C++26)
      1) Value-initializesbase_ via its default member initializer (= V()).
      2) Initializesbase_ withstd::move(base).

      Parameters

      base - a view

      std::ranges::cache_latest_view::base

      constexpr V base()const& requiresstd::copy_constructible<V>;
      		 (1)(since C++26)
      constexpr V base()&&;
      		 (2)(since C++26)
      1) Copy-constructs the result from the underlying view. Equivalent toreturn base_;.
      2) Move-constructs the result from the underlying view. Equivalent toreturn std::move(base_);.

      std::ranges::cache_latest_view::begin

      constexprauto begin();
      		(since C++26)

      Equivalent toreturn/*iterator*/(*this);.

      std::ranges::cache_latest_view::end

      constexprauto end();
      		(since C++26)

      Equivalent toreturn/*sentinel*/(*this);.

      std::ranges::cache_latest_view::size

      constexprauto size() requiresranges::sized_range<V>;
      		 (1)(since C++26)
      constexprauto size()const requiresranges::sized_range<const V>;
      		 (2)(since C++26)
      1,2) Equivalent toreturnranges::size(base_);

      [edit]Deduction guides

      template<class R>
      cache_latest_view( R&&)-> cache_latest_view<views::all_t<R>>;
      		(since C++26)

      [edit]Nested classes

      the iterator type
      (exposition-only member class template*)
      the sentinel type
      (exposition-only member class template*)

      [edit]Notes

      cache_latest_view is useful if the computation of the element to produce is expensive.

      Feature-test macroValueStdFeature
      __cpp_lib_ranges_cache_latest202411L(C++26)std::ranges::cache_latest_view

      [edit]Example

      Run this code
      #include <algorithm>#include <print>#include <ranges> int main(){constauto v={1,2,3,4,5}; auto square=[](int i){std::print("transform: {} ", i);return i* i;}; auto is_even=[](int i){std::print("filter: {} ", i);return i%2==0;}; auto print=[](auto v){        std::ranges::for_each(v,[](int i){std::println("Got: {}", i);});std::println();}; std::println("Without caching latest (note recalculations):");auto even_squares= v| std::views::transform(square)| std::views::filter(is_even);    print(even_squares); std::println("With caching latest:");auto fast_even_squares= v| std::views::transform(square)| std::views::cache_latest| std::views::filter(is_even);    print(fast_even_squares);}

      Output:

      Without caching latest (note recalculations):transform: 1 filter: 1 transform: 2 filter: 4 transform: 2 Got: 4transform: 3 filter: 9 transform: 4 filter: 16 transform: 4 Got: 16transform: 5 filter: 25 With caching latest:transform: 1 filter: 1 transform: 2 filter: 4 Got: 4transform: 3 filter: 9 transform: 4 filter: 16 Got: 16transform: 5 filter: 25
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/ranges/cache_latest_view&oldid=181223"
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