add boost on mac

macx64/include/boost/histogram/detail/compressed_pair.hpp

@@ -0,0 +1,74 @@
+// Copyright 2018 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_DETAIL_COMPRESSED_PAIR_HPP
+#define BOOST_HISTOGRAM_DETAIL_COMPRESSED_PAIR_HPP
+
+#include <type_traits>
+#include <utility>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+
+template <typename T1, typename T2, bool B>
+class compressed_pair_impl;
+
+template <typename T1, typename T2>
+class compressed_pair_impl<T1, T2, true> : protected T2 {
+public:
+  template <typename U1, typename U2>
+  compressed_pair_impl(U1&& u1, U2&& u2)
+      : T2(std::forward<U2>(u2)), first_(std::forward<U1>(u1)) {}
+  template <typename U1>
+  compressed_pair_impl(U1&& u1) : first_(std::forward<U1>(u1)) {}
+  compressed_pair_impl() = default;
+
+  T1& first() { return first_; }
+  T2& second() { return static_cast<T2&>(*this); }
+  const T1& first() const { return first_; }
+  const T2& second() const { return static_cast<const T2&>(*this); }
+
+private:
+  T1 first_;
+};
+
+template <typename T1, typename T2>
+class compressed_pair_impl<T1, T2, false> {
+public:
+  template <typename U1, typename U2>
+  compressed_pair_impl(U1&& u1, U2&& u2)
+      : first_(std::forward<U1>(u1)), second_(std::forward<U2>(u2)) {}
+  template <typename U1>
+  compressed_pair_impl(U1&& u1) : first_(std::forward<U1>(u1)) {}
+  compressed_pair_impl() = default;
+
+  T1& first() { return first_; }
+  T2& second() { return second_; }
+  const T1& first() const { return first_; }
+  const T2& second() const { return second_; }
+
+private:
+  T1 first_;
+  T2 second_;
+};
+
+template <typename... Ts>
+void swap(compressed_pair_impl<Ts...>& a, compressed_pair_impl<Ts...>& b) {
+  using std::swap;
+  swap(a.first(), b.first());
+  swap(a.second(), b.second());
+}
+
+template <typename T1, typename T2>
+using compressed_pair =
+    compressed_pair_impl<T1, T2, (!std::is_final<T2>::value && std::is_empty<T2>::value)>;
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif