adapter.hpp

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/**
 * @file
 * @ingroup ipcq
 * @brief Provides iterator adapter for `ipcq::BasicReader`.
 * @copyright
 *   SPDX-FileCopyrightText: 2020-2020 European Southern Observatory (ESO)
 *
 *   SPDX-License-Identifier: LGPL-3.0-only
 */
#ifndef IPCQ_ADAPTER_HPP_
#define IPCQ_ADAPTER_HPP_
#include <iterator>
 
namespace ipcq {
 
/**
 * Primary template for @a InputIterators.
 * This IteratorTraits::value_type is the container type even for @a OutputIterators.
 *
 * @ingroup ipcq
 */
template <class Iterator, class=void>
struct IteratorTraits : std::iterator_traits<Iterator>{
};
 
/**
 * Template specialization for @a OutputIterators for which normal std::iterator_traits::value_type
 * is void.
 *
 * @ingroup ipcq
 */
template <class Iterator>
struct IteratorTraits<Iterator, std::void_t<typename Iterator::container_type>>
    : std::iterator_traits<typename Iterator::container_type::iterator> {
};
 
/**
 * Adapts either @a @c LegacyOutputIterator or @a @c Iterator type (e.g. @c
 * std::back_insert_iterator or @c std::iterator) to use in @c BasicReader::Read and @c
 * BasicReader::Read.
 *
 * Example that does in-place assignment:
 *
 *     std::vector<Topic> buffer(5);
 *     reader.Read(ipcq::OutputIteratorAdapter(std::begin(buffer)), 5, 5s);
 *
 * @see ipcq::BackInserter for the variant that does insertion with @c Container::push_back.
 *
 * @ingroup ipcq
 */
template <class Iterator>
struct OutputIteratorAdapter {
    using ValueType = typename IteratorTraits<Iterator>::value_type;
 
    constexpr OutputIteratorAdapter(Iterator iter) : iterator(std::move(iter)) {
    }
 
    /**
     * Assigns @c value to *iterator and then increments the iterator.
     *
     * @code *iterator++ = value; @endcode
     *
     */
    constexpr void operator()(ValueType const& value) {
        *iterator++ = value;
    }
    Iterator iterator;
};
 
/**
 * Convenience function that creates an OutputIteratorAdapter with a `std::back_insert_iterator` for
 * a container.
 *
 * Equivalent to:
 *
 *     OutputIteratorAdapter(std::back_insert_iterator(container));
 *
 * Example:
 *
 *     std::vector<Topic> buffer;
 *     buffer.reserve(BATCH_SIZE);
 *     reader.Read(ipcq::BackInserter(buffer), BATCH_SIZE, 5s);
 *
 * @sa ipcq::OutputIteratorAdapter
 *
 * @ingroup ipcq
 */
template <class Container>
constexpr auto
BackInserter(Container& c) -> OutputIteratorAdapter<std::back_insert_iterator<Container>> {
    using Iterator = std::back_insert_iterator<Container>;
    return OutputIteratorAdapter<Iterator>(Iterator{c});
}
 
}  // namespace ipcq
 
#endif  // #ifndef IPCQ_ADAPTER_HPP_