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Allow use of
operator-> with huffman::table::const_iterator
Replace use of `views::transform` with a custom view type `detail::base_view<V, B>` that casts a derived type (i.e. elements of view `V`) to base `B`. `detail::base_view<V, B>` requires the reference type of underlying view `V` be a true reference, thus `detail::base_view<V, B>::iterator` defines `operator->` to return a pointer to `B*`. resolves #49 Change-Id: I2c9d14705bd5a0d8f7e562006913906d40c7fe86
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,171 @@ | ||
| #pragma once | ||
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| #include <concepts> | ||
| #include <iterator> | ||
| #include <ranges> | ||
| #include <utility> | ||
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| namespace gpu_deflate::huffman::detail { | ||
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| /// A view of elements cast to a base class | ||
| /// @tparam V underlying view | ||
| /// @tparam B base class | ||
| /// | ||
| template <std::ranges::forward_range V, class B> | ||
| requires std::ranges::view<V> and | ||
| std::same_as<std::ranges::iterator_t<V>, | ||
| std::ranges::sentinel_t<V>> and | ||
| std::derived_from<std::ranges::range_value_t<V>, B> | ||
| class base_view : public std::ranges::view_interface<base_view<V, B>> | ||
| { | ||
| // This is largely adapted from `transform_view` (or other views), although we | ||
| // apply some simplifications: | ||
| // * V must model `forward_range` instead of `input_range` | ||
| // * sentinel_t<V> is the same as iterator_t<V> | ||
| // | ||
| // https://eel.is/c++draft/range.transform | ||
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| V base_{}; | ||
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| public: | ||
| class iterator | ||
| { | ||
| using base_iterator = std::ranges::iterator_t<V>; | ||
| base_iterator base_{}; | ||
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| public: | ||
| using iterator_category = | ||
| typename std::iterator_traits<base_iterator>::iterator_category; | ||
| using value_type = std::ranges::range_value_t<V>; | ||
| using reference = B&; | ||
| using pointer = B*; | ||
| using difference_type = std::ranges::range_difference_t<V>; | ||
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| iterator() | ||
| requires std::default_initializable<base_iterator> | ||
| = default; | ||
| constexpr iterator(base_iterator current) : base_{std::move(current)} {} | ||
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| constexpr auto base() const& noexcept -> const base_iterator& | ||
| { | ||
| return base_; | ||
| } | ||
| constexpr auto base() && -> base_iterator { return std::move(base_); } | ||
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| constexpr auto operator*() const -> reference | ||
| { | ||
| return static_cast<reference>(*base_); | ||
| } | ||
| constexpr auto operator->() const -> pointer { return &**this; } | ||
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| constexpr auto operator++() -> iterator& | ||
| { | ||
| ++base_; | ||
| return *this; | ||
| } | ||
| constexpr auto operator++(int) -> iterator | ||
| { | ||
| auto tmp = *this; | ||
| ++*this; | ||
| return tmp; | ||
| } | ||
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| constexpr auto operator--() -> iterator& | ||
| requires std::ranges::bidirectional_range<V> | ||
| { | ||
| --base_; | ||
| return *this; | ||
| } | ||
| constexpr auto operator--(int) -> iterator | ||
| requires std::ranges::bidirectional_range<V> | ||
| { | ||
| auto tmp = *this; | ||
| --*this; | ||
| return tmp; | ||
| } | ||
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| constexpr auto operator+=(difference_type n) -> iterator& | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| base_ += n; | ||
| return *this; | ||
| } | ||
| constexpr auto operator-=(difference_type n) -> iterator& | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| base_ -= n; | ||
| return *this; | ||
| } | ||
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| constexpr auto operator[](difference_type n) const -> reference | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| return static_cast<reference>(base_[n]); | ||
| } | ||
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| friend constexpr auto | ||
| operator<=>(const iterator&, const iterator&) = default; | ||
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| friend constexpr auto operator+(iterator i, difference_type n) -> iterator | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| return i += n; | ||
| } | ||
| friend constexpr auto operator+(difference_type n, iterator i) -> iterator | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| return i + n; | ||
| } | ||
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| friend constexpr auto operator-(iterator i, difference_type n) -> iterator | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| return i -= n; | ||
| } | ||
| friend constexpr auto | ||
| operator-(const iterator& x, const iterator& y) -> difference_type | ||
| requires std::ranges::random_access_range<V> | ||
| { | ||
| return x.base() - y.base(); | ||
| } | ||
| }; | ||
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| base_view() | ||
| requires std::default_initializable<V> | ||
| = default; | ||
| constexpr explicit base_view(V base) : base_{std::move(base)} {} | ||
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| constexpr auto base() const& -> V | ||
| requires std::copy_constructible<V> | ||
| { | ||
| return base_; | ||
| } | ||
| constexpr auto base() && -> V { return std::move(base_); } | ||
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| constexpr auto begin() const -> iterator { return {base().begin()}; } | ||
| constexpr auto end() const -> iterator { return {base().end()}; } | ||
| }; | ||
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| // Use of range_adaptor_clousure requires GCC 13 or LLVM > 16.0.0 | ||
| // While this isn't necessary, it does allow a simpler declaration of | ||
| // `base_view_` type in the `table` class template. | ||
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| // namespace views { | ||
| // | ||
| // template <class B> | ||
| // struct base_raco : std::ranges::range_adaptor_closure<base_raco<B>> | ||
| //{ | ||
| // template <std::ranges::forward_range V> | ||
| // constexpr auto operator()(V v) const | ||
| // -> base_view<V, B> | ||
| // { | ||
| // return base_view<V, B>{v} | ||
| // } | ||
| //}; | ||
| // | ||
| // template <class B> | ||
| // inline constexpr auto base = base_raco<B>{}; | ||
| // | ||
| //} | ||
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| } // namespace gpu_deflate::huffman::detail |
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