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85 lines
3.2 KiB
C++
85 lines
3.2 KiB
C++
#pragma once
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#include <iterator>
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#include <type_traits>
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namespace ext
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{
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/// \brief Strip type off top level reference and cv-qualifiers thus allowing storage in containers
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template <typename T>
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using unqualified_t = std::remove_cv_t<std::remove_reference_t<T>>;
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template <typename It, typename Mapper>
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using apply_t = typename std::result_of<Mapper(typename It::reference)>::type;
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template <typename It, typename Mapper>
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struct map_iterator : std::iterator<
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typename It::iterator_category,
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std::remove_reference_t<apply_t<It, Mapper>>,
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std::ptrdiff_t,
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std::add_pointer_t<std::remove_reference_t<apply_t<It, Mapper>>>,
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apply_t<It, Mapper>>
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{
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using base_iterator = std::iterator<
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typename It::iterator_category,
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std::remove_reference_t<apply_t<It, Mapper>>,
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std::ptrdiff_t,
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std::add_pointer<std::remove_reference_t<apply_t<It, Mapper>>>,
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apply_t<It, Mapper>>;
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It current;
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Mapper mapper;
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map_iterator(const It it, const Mapper mapper) : current{it}, mapper{mapper} {}
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typename base_iterator::reference operator*() { return mapper(*current); }
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map_iterator & operator++() { return ++current, *this; }
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map_iterator & operator--() { return --current, *this; }
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bool operator==(const map_iterator & other) { return current == other.current; }
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bool operator!=(const map_iterator & other) { return current != other.current; }
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typename base_iterator::difference_type operator-(const map_iterator & other) { return current - other.current; }
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};
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template <typename It, typename Mapper>
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auto make_map_iterator(const It it, const Mapper mapper) -> ext::map_iterator<It, Mapper>
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{
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return { it, mapper };
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}
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/** \brief Returns collection of the same container-type as the input collection,
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* with each element transformed by the application of `mapper`. */
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template <template <typename...> class Collection, typename... Params, typename Mapper>
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auto map(const Collection<Params...> & collection, const Mapper mapper)
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{
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using value_type = unqualified_t<decltype(mapper(*std::begin(collection)))>;
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return Collection<value_type>(ext::make_map_iterator(std::begin(collection), mapper),
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ext::make_map_iterator(std::end(collection), mapper));
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};
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/** \brief Returns collection of specified container-type,
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* with each element transformed by the application of `mapper`.
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* Allows conversion between different container-types, e.g. std::vector to std::list */
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template <template <typename...> class ResultCollection, typename Collection, typename Mapper>
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auto map(const Collection & collection, const Mapper mapper)
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{
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using value_type = unqualified_t<decltype(mapper(*std::begin(collection)))>;
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return ResultCollection<value_type>(ext::make_map_iterator(std::begin(collection), mapper),
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ext::make_map_iterator(std::end(collection), mapper));
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};
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/** \brief Returns collection of specified type,
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* with each element transformed by the application of `mapper`.
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* Allows leveraging implicit conversion between the result of applying `mapper` and R::value_type. */
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template <typename ResultCollection, typename Collection, typename Mapper>
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auto map(const Collection & collection, const Mapper mapper)
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{
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return ResultCollection(ext::make_map_iterator(std::begin(collection), mapper),
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ext::make_map_iterator(std::end(collection), mapper));
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}
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}
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