// Copyright 2019 Hans Dembinski
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_HISTOGRAM_AXIS_METADATA_BASE_HPP
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#define BOOST_HISTOGRAM_AXIS_METADATA_BASE_HPP
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#include <boost/histogram/axis/traits.hpp>
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#include <boost/histogram/detail/replace_type.hpp>
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#include <string>
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#include <type_traits>
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namespace boost {
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namespace histogram {
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namespace axis {
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/** Meta data holder with space optimization for empty meta data types.
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Allows write-access to metadata even if const.
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@tparam Metadata Wrapped meta data type.
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*/
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template <class Metadata, bool Detail>
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class metadata_base {
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protected:
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using metadata_type = Metadata;
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// std::string explicitly guarantees nothrow only in C++17
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static_assert(std::is_same<metadata_type, std::string>::value ||
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std::is_nothrow_move_constructible<metadata_type>::value,
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"metadata must be nothrow move constructible");
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metadata_base() = default;
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metadata_base(const metadata_base&) = default;
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metadata_base& operator=(const metadata_base&) = default;
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// make noexcept because std::string is nothrow move constructible only in C++17
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metadata_base(metadata_base&& o) noexcept : data_(std::move(o.data_)) {}
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metadata_base(metadata_type&& o) noexcept : data_(std::move(o)) {}
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// make noexcept because std::string is nothrow move constructible only in C++17
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metadata_base& operator=(metadata_base&& o) noexcept {
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data_ = std::move(o.data_);
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return *this;
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}
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private:
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mutable metadata_type data_;
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public:
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/// Returns reference to metadata.
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metadata_type& metadata() noexcept { return data_; }
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/// Returns reference to mutable metadata from const axis.
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metadata_type& metadata() const noexcept { return data_; }
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};
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#ifndef BOOST_HISTOGRAM_DOXYGEN_INVOKED
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// specialization for empty metadata
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template <class Metadata>
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class metadata_base<Metadata, true> {
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protected:
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using metadata_type = Metadata;
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metadata_base() = default;
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metadata_base(metadata_type&&) {}
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metadata_base& operator=(metadata_type&&) { return *this; }
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public:
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metadata_type& metadata() noexcept {
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return static_cast<const metadata_base&>(*this).metadata();
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}
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metadata_type& metadata() const noexcept {
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static metadata_type data;
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return data;
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}
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};
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template <class Metadata, class Detail = detail::replace_default<Metadata, std::string>>
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using metadata_base_t =
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metadata_base<Detail, (std::is_empty<Detail>::value && std::is_final<Detail>::value)>;
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#endif
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} // namespace axis
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} // namespace histogram
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} // namespace boost
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#endif
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