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Telegram/ThirdParty/range-v3/include/range/v3/view/generate.hpp

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+/// \file
+// Range v3 library
+//
+//  Copyright Eric Niebler 2014-present
+//
+//  Use, modification and distribution is subject to the
+//  Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+// Project home: https://github.com/ericniebler/range-v3
+//
+
+#ifndef RANGES_V3_VIEW_GENERATE_HPP
+#define RANGES_V3_VIEW_GENERATE_HPP
+
+#include <type_traits>
+#include <utility>
+
+#include <meta/meta.hpp>
+
+#include <range/v3/range_fwd.hpp>
+
+#include <range/v3/functional/invoke.hpp>
+#include <range/v3/iterator/unreachable_sentinel.hpp>
+#include <range/v3/range/access.hpp>
+#include <range/v3/range/primitives.hpp>
+#include <range/v3/range/traits.hpp>
+#include <range/v3/utility/optional.hpp>
+#include <range/v3/utility/semiregular_box.hpp>
+#include <range/v3/utility/static_const.hpp>
+#include <range/v3/view/facade.hpp>
+
+#include <range/v3/detail/prologue.hpp>
+
+namespace ranges
+{
+    /// \addtogroup group-views
+    /// @{
+    template<typename G>
+    struct generate_view : view_facade<generate_view<G>, infinite>
+    {
+    private:
+        friend range_access;
+        using result_t = invoke_result_t<G &>;
+        semiregular_box_t<G> gen_;
+        detail::non_propagating_cache<result_t> val_;
+        struct cursor
+        {
+        private:
+            generate_view * view_;
+
+        public:
+            cursor() = default;
+            explicit cursor(generate_view * view)
+              : view_(view)
+            {}
+            result_t && read() const
+            {
+                if(!view_->val_)
+                    view_->val_.emplace(view_->gen_());
+                return static_cast<result_t &&>(static_cast<result_t &>(*view_->val_));
+            }
+            void next()
+            {
+                if(view_->val_)
+                    view_->val_.reset();
+                else
+                    static_cast<void>(view_->gen_());
+            }
+        };
+        cursor begin_cursor()
+        {
+            return cursor{this};
+        }
+        unreachable_sentinel_t end_cursor() const
+        {
+            return {};
+        }
+
+    public:
+        generate_view() = default;
+        explicit generate_view(G g)
+          : gen_(std::move(g))
+        {}
+        result_t & cached()
+        {
+            return *val_;
+        }
+    };
+
+    namespace views
+    {
+        struct generate_fn
+        {
+            template(typename G)(
+                requires invocable<G &> AND copy_constructible<G> AND
+                    std::is_object<detail::decay_t<invoke_result_t<G &>>>::value AND
+                    constructible_from<detail::decay_t<invoke_result_t<G &>>,
+                                       invoke_result_t<G &>> AND
+                    assignable_from<detail::decay_t<invoke_result_t<G &>> &,
+                                    invoke_result_t<G &>>)
+            generate_view<G> operator()(G g) const
+            {
+                return generate_view<G>{std::move(g)};
+            }
+        };
+
+        /// \relates generate_fn
+        /// \ingroup group-views
+        RANGES_INLINE_VARIABLE(generate_fn, generate)
+    } // namespace views
+    /// \@}
+} // namespace ranges
+
+#include <range/v3/detail/epilogue.hpp>
+#include <range/v3/detail/satisfy_boost_range.hpp>
+RANGES_SATISFY_BOOST_RANGE(::ranges::generate_view)
+
+#endif