ClickHouse/libs/libcommon/include/ext/map.hpp

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2015-10-05 00:33:43 +00:00
#pragma once
#include <iterator>
#include <type_traits>
namespace ext
{
/// \brief Strip type off top level reference and cv-qualifiers thus allowing storage in containers
template <typename T>
using unqualified_t = std::remove_cv_t<std::remove_reference_t<T>>;
template <typename It, typename Mapper>
using apply_t = typename std::result_of<Mapper(typename It::reference)>::type;
template <typename It, typename Mapper>
struct map_iterator : std::iterator<
typename It::iterator_category,
std::remove_reference_t<apply_t<It, Mapper>>,
std::ptrdiff_t,
std::add_pointer_t<std::remove_reference_t<apply_t<It, Mapper>>>,
apply_t<It, Mapper>>
{
using base_iterator = std::iterator<
typename It::iterator_category,
std::remove_reference_t<apply_t<It, Mapper>>,
std::ptrdiff_t,
std::add_pointer<std::remove_reference_t<apply_t<It, Mapper>>>,
apply_t<It, Mapper>>;
It current;
Mapper mapper;
map_iterator(const It it, const Mapper mapper) : current{it}, mapper{mapper} {}
typename base_iterator::reference operator*() { return mapper(*current); }
map_iterator & operator++() { return ++current, *this; }
map_iterator & operator--() { return --current, *this; }
bool operator==(const map_iterator & other) { return current == other.current; }
bool operator!=(const map_iterator & other) { return current != other.current; }
typename base_iterator::difference_type operator-(const map_iterator & other) { return current - other.current; }
};
template <typename It, typename Mapper>
auto make_map_iterator(const It it, const Mapper mapper) -> ext::map_iterator<It, Mapper>
{
return { it, mapper };
}
/** \brief Returns collection of the same container-type as the input collection,
* with each element transformed by the application of `mapper`. */
template <template <typename...> class Collection, typename... Params, typename Mapper>
auto map(const Collection<Params...> & collection, const Mapper mapper)
{
using value_type = unqualified_t<decltype(mapper(*std::begin(collection)))>;
return Collection<value_type>(ext::make_map_iterator(std::begin(collection), mapper),
ext::make_map_iterator(std::end(collection), mapper));
};
/** \brief Returns collection of specified container-type,
* with each element transformed by the application of `mapper`.
* Allows conversion between different container-types, e.g. std::vector to std::list */
template <template <typename...> class ResultCollection, typename Collection, typename Mapper>
auto map(const Collection & collection, const Mapper mapper)
{
using value_type = unqualified_t<decltype(mapper(*std::begin(collection)))>;
return ResultCollection<value_type>(ext::make_map_iterator(std::begin(collection), mapper),
ext::make_map_iterator(std::end(collection), mapper));
};
/** \brief Returns collection of specified type,
* with each element transformed by the application of `mapper`.
* Allows leveraging implicit conversion between the result of applying `mapper` and R::value_type. */
template <typename ResultCollection, typename Collection, typename Mapper>
auto map(const Collection & collection, const Mapper mapper)
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{
return ResultCollection(ext::make_map_iterator(std::begin(collection), mapper),
ext::make_map_iterator(std::end(collection), mapper));
}
}