Add std::hash specialization

include/boost/optional/detail/optional_hash.hpp

@@ -0,0 +1,49 @@
+// Copyright (C) 2022 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_DETAIL_OPTIONAL_HASH_AJK_20MAY2022_HPP
+#define BOOST_OPTIONAL_DETAIL_OPTIONAL_HASH_AJK_20MAY2022_HPP
+
+#include <boost/optional/optional_fwd.hpp>
+#include <boost/config.hpp>
+
+#if !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH) && !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+#include <functional>
+
+namespace std
+{
+  template <typename T>
+  struct hash<boost::optional<T> >
+  {
+    typedef typename hash<T>::result_type result_type;
+    typedef boost::optional<T> argument_type;
+
+    BOOST_CONSTEXPR result_type operator()(const argument_type& arg) const {
+      return arg ? std::hash<T>()(*arg) : result_type();
+    }
+  };
+
+  template <typename T>
+  struct hash<boost::optional<T&> >
+  {
+    typedef typename hash<T>::result_type result_type;
+    typedef boost::optional<T&> argument_type;
+
+    BOOST_CONSTEXPR result_type operator()(const argument_type& arg) const {
+      return arg ? std::hash<T>()(*arg) : result_type();
+    }
+  };
+}
+
+#endif // !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH) && !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+#endif // header guard

include/boost/optional/optional.hpp

@@ -65,6 +65,7 @@
 #include <boost/optional/detail/optional_config.hpp>
 #include <boost/optional/detail/optional_factory_support.hpp>
 #include <boost/optional/detail/optional_aligned_storage.hpp>
+#include <boost/optional/detail/optional_hash.hpp>
 
 namespace boost { namespace optional_detail {
 

test/Jamfile.v2

@@ -26,6 +26,7 @@ import testing ;
     [ run optional_test_empty_braces.cpp ]
     [ run optional_test_make_optional.cpp ]
     [ run optional_test_flat_map.cpp ]
+    [ run optional_test_hash.cpp ]
     [ run optional_test_map.cpp ]
     [ run optional_test_tie.cpp ]
     [ run optional_test_ref_assign_portable_minimum.cpp ]

test/optional_test_hash.cpp

@@ -0,0 +1,64 @@
+// Copyright (C) 2014 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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)
+//
+// See http://www.boost.org/lib/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#include "boost/optional/optional.hpp"
+#include "boost/config.hpp"
+#include "boost/core/lightweight_test.hpp"
+
+#if !defined(BOOST_NO_CXX11_HDR_UNORDERED_SET) && !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH)
+
+#include <unordered_set>
+
+void test_unordered_map()
+{
+  std::unordered_set<boost::optional<int> > set;
+  set.insert(boost::optional<int>(1));
+  set.insert(boost::optional<int>(1));
+
+
+  BOOST_TEST(set.size() == 1u);
+  BOOST_TEST(set.find(boost::optional<int>(1)) != set.end());
+}
+
+#else
+
+void test_unordered_map()
+{}
+
+#endif
+
+
+#if !defined(BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH) && !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+void tets_hash()
+{
+  std::hash<boost::optional<int> > hash_int;
+  boost::optional<int> oN;
+  boost::optional<int> o1(1);
+
+  BOOST_TEST(hash_int(oN) == hash_int(oN));
+  BOOST_TEST(hash_int(o1) == hash_int(o1));
+}
+
+#else
+
+void tets_hash()
+{}
+
+#endif
+
+
+int main()
+{
+  test_unordered_map();
+  tets_hash();
+  return boost::report_errors();
+}