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Make TransformView iterator's category match its underlying's

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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.
This commit is contained in:
Maxime Coste 2018-07-26 20:58:55 +10:00
parent 62fa783bfd
commit 0919679e0d
1 changed files with 32 additions and 21 deletions
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53
src/ranges.hh
View File

@ -82,8 +82,8 @@ struct FilterView
struct Iterator : std::iterator<std::forward_iterator_tag,
typename std::iterator_traits<RangeIt>::value_type>
{
Iterator(const FilterView& view, RangeIt it, RangeIt end)
: m_it{std::move(it)}, m_end{std::move(end)}, m_view{&view}
Iterator(Filter& filter, RangeIt it, RangeIt end)
: m_it{std::move(it)}, m_end{std::move(end)}, m_filter{&filter}
{
do_filter();
}
@ -107,17 +107,17 @@ struct FilterView
private:
void do_filter()
{
while (m_it != m_end and not m_view->m_filter(*m_it))
while (m_it != m_end and not (*m_filter)(*m_it))
++m_it;
}
RangeIt m_it;
RangeIt m_end;
const FilterView* m_view;
Filter* m_filter;
};
Iterator begin() const { return {*this, std::begin(m_range), std::end(m_range)}; }
Iterator end() const { return {*this, std::end(m_range), std::end(m_range)}; }
Iterator begin() const { return {m_filter, std::begin(m_range), std::end(m_range)}; }
Iterator end() const { return {m_filter, std::end(m_range), std::end(m_range)}; }
Range m_range;
mutable Filter m_filter;
@ -138,34 +138,45 @@ struct TransformView
using RangeIt = IteratorOf<Range>;
using ResType = decltype(std::declval<Transform>()(*std::declval<RangeIt>()));
struct Iterator : std::iterator<std::forward_iterator_tag, std::remove_reference_t<ResType>>
struct Iterator
{
Iterator(const TransformView& view, RangeIt it)
: m_it{std::move(it)}, m_view{&view} {}
using iterator_category = typename std::iterator_traits<RangeIt>::iterator_category;
using value_type = std::remove_reference_t<ResType>;
using difference_type = typename std::iterator_traits<RangeIt>::difference_type;
using pointer = value_type*;
using reference = value_type&;
Iterator(Transform& transform, RangeIt it)
: m_it{std::move(it)}, m_transform{&transform} {}
decltype(auto) operator*() { return (*m_transform)(*m_it); }
decltype(auto) operator[](difference_type i) const { return (*m_transform)(m_it[i]); }
decltype(auto) operator*() { return m_view->m_transform(*m_it); }
Iterator& operator++() { ++m_it; return *this; }
Iterator operator++(int) { auto copy = *this; ++m_it; return copy; }
friend bool operator==(const Iterator& lhs, const Iterator& rhs)
{
return lhs.m_it == rhs.m_it;
}
Iterator& operator--() { --m_it; return *this; }
Iterator operator--(int) { auto copy = *this; --m_it; return copy; }
friend bool operator!=(const Iterator& lhs, const Iterator& rhs)
{
return not (lhs == rhs);
}
Iterator& operator+=(difference_type diff) { m_it += diff; return *this; }
Iterator& operator-=(difference_type diff) { m_it -= diff; return *this; }
Iterator operator+(difference_type diff) { return {*m_transform, m_it + diff}; }
Iterator operator-(difference_type diff) { return {*m_transform, m_it - diff}; }
friend bool operator==(const Iterator& lhs, const Iterator& rhs) { return lhs.m_it == rhs.m_it; }
friend bool operator!=(const Iterator& lhs, const Iterator& rhs) { return not (lhs == rhs); }
friend difference_type operator-(const Iterator& lhs, const Iterator& rhs) { return lhs.m_it - rhs.m_it; }
RangeIt base() const { return m_it; }
private:
RangeIt m_it;
const TransformView* m_view;
Transform* m_transform;
};
Iterator begin() const { return {*this, std::begin(m_range)}; }
Iterator end() const { return {*this, std::end(m_range)}; }
Iterator begin() const { return {m_transform, std::begin(m_range)}; }
Iterator end() const { return {m_transform, std::end(m_range)}; }
Range m_range;
mutable Transform m_transform;