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