Make TransformView iterator's category match its underlying's
In particular, this make gathering a transformed range to a vector faster because we can use the random access nature of underlying iterator to get the size to allocate in the vector upfront.
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@ -82,8 +82,8 @@ struct FilterView
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struct Iterator : std::iterator<std::forward_iterator_tag,
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typename std::iterator_traits<RangeIt>::value_type>
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{
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Iterator(const FilterView& view, RangeIt it, RangeIt end)
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: m_it{std::move(it)}, m_end{std::move(end)}, m_view{&view}
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Iterator(Filter& filter, RangeIt it, RangeIt end)
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: m_it{std::move(it)}, m_end{std::move(end)}, m_filter{&filter}
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{
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do_filter();
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}
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@ -107,17 +107,17 @@ struct FilterView
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private:
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void do_filter()
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{
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while (m_it != m_end and not m_view->m_filter(*m_it))
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while (m_it != m_end and not (*m_filter)(*m_it))
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++m_it;
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}
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RangeIt m_it;
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RangeIt m_end;
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const FilterView* m_view;
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Filter* m_filter;
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};
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Iterator begin() const { return {*this, std::begin(m_range), std::end(m_range)}; }
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Iterator end() const { return {*this, std::end(m_range), std::end(m_range)}; }
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Iterator begin() const { return {m_filter, std::begin(m_range), std::end(m_range)}; }
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Iterator end() const { return {m_filter, std::end(m_range), std::end(m_range)}; }
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Range m_range;
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mutable Filter m_filter;
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@ -138,34 +138,45 @@ struct TransformView
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using RangeIt = IteratorOf<Range>;
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using ResType = decltype(std::declval<Transform>()(*std::declval<RangeIt>()));
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struct Iterator : std::iterator<std::forward_iterator_tag, std::remove_reference_t<ResType>>
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struct Iterator
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{
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Iterator(const TransformView& view, RangeIt it)
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: m_it{std::move(it)}, m_view{&view} {}
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using iterator_category = typename std::iterator_traits<RangeIt>::iterator_category;
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using value_type = std::remove_reference_t<ResType>;
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using difference_type = typename std::iterator_traits<RangeIt>::difference_type;
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using pointer = value_type*;
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using reference = value_type&;
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Iterator(Transform& transform, RangeIt it)
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: m_it{std::move(it)}, m_transform{&transform} {}
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decltype(auto) operator*() { return (*m_transform)(*m_it); }
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decltype(auto) operator[](difference_type i) const { return (*m_transform)(m_it[i]); }
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decltype(auto) operator*() { return m_view->m_transform(*m_it); }
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Iterator& operator++() { ++m_it; return *this; }
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Iterator operator++(int) { auto copy = *this; ++m_it; return copy; }
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friend bool operator==(const Iterator& lhs, const Iterator& rhs)
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{
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return lhs.m_it == rhs.m_it;
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}
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Iterator& operator--() { --m_it; return *this; }
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Iterator operator--(int) { auto copy = *this; --m_it; return copy; }
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friend bool operator!=(const Iterator& lhs, const Iterator& rhs)
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{
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return not (lhs == rhs);
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}
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Iterator& operator+=(difference_type diff) { m_it += diff; return *this; }
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Iterator& operator-=(difference_type diff) { m_it -= diff; return *this; }
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Iterator operator+(difference_type diff) { return {*m_transform, m_it + diff}; }
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Iterator operator-(difference_type diff) { return {*m_transform, m_it - diff}; }
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friend bool operator==(const Iterator& lhs, const Iterator& rhs) { return lhs.m_it == rhs.m_it; }
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friend bool operator!=(const Iterator& lhs, const Iterator& rhs) { return not (lhs == rhs); }
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friend difference_type operator-(const Iterator& lhs, const Iterator& rhs) { return lhs.m_it - rhs.m_it; }
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RangeIt base() const { return m_it; }
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private:
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RangeIt m_it;
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const TransformView* m_view;
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Transform* m_transform;
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};
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Iterator begin() const { return {*this, std::begin(m_range)}; }
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Iterator end() const { return {*this, std::end(m_range)}; }
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Iterator begin() const { return {m_transform, std::begin(m_range)}; }
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Iterator end() const { return {m_transform, std::end(m_range)}; }
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Range m_range;
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mutable Transform m_transform;
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