std::optional support

include/boost/container_hash/hash/hash.hpp

@@ -230,6 +230,11 @@ namespace boost
     template <typename T>
     typename boost::hash_detail::float_numbers<T>::type hash_value(T);
 
+#if BOOST_HASH_HAS_OPTIONAL
+    template <typename T>
+    std::size_t hash_value(std::optional<T> const&);
+#endif
+
 #if !defined(BOOST_NO_CXX11_HDR_TYPEINDEX)
     std::size_t hash_value(std::type_index);
 #endif
@@ -481,6 +486,19 @@ namespace boost
         return boost::hash_detail::float_hash_value(v);
     }
 
+#if BOOST_HASH_HAS_OPTIONAL
+    template <typename T>
+    inline std::size_t hash_value(std::optional<T> const& v) {
+        if (!v) {
+            // Arbitray value for empty optional.
+            return 0x12345678;
+        } else {
+            boost::hash<T> hf;
+            return hf(*v);
+        }
+    }
+#endif
+
 #if !defined(BOOST_NO_CXX11_HDR_TYPEINDEX)
     inline std::size_t hash_value(std::type_index v)
     {
@@ -540,6 +558,16 @@ namespace boost
         } \
     };
 
+#define BOOST_HASH_SPECIALIZE_TEMPLATE_REF(type) \
+    struct hash<type> \
+         : public boost::hash_detail::hash_base<type> \
+    { \
+        std::size_t operator()(type const& v) const \
+        { \
+            return boost::hash_value(v); \
+        } \
+    };
+
     BOOST_HASH_SPECIALIZE(bool)
     BOOST_HASH_SPECIALIZE(char)
     BOOST_HASH_SPECIALIZE(signed char)
@@ -598,12 +626,18 @@ namespace boost
     BOOST_HASH_SPECIALIZE(boost::uint128_type)
 #endif
 
+#if BOOST_HASH_HAS_OPTIONAL
+    template <typename T>
+    BOOST_HASH_SPECIALIZE_TEMPLATE_REF(std::optional<T>)
+#endif
+
 #if !defined(BOOST_NO_CXX11_HDR_TYPEINDEX)
     BOOST_HASH_SPECIALIZE(std::type_index)
 #endif
 
 #undef BOOST_HASH_SPECIALIZE
 #undef BOOST_HASH_SPECIALIZE_REF
+#undef BOOST_HASH_SPECIALIZE_TEMPLATE_REF
 
 // Specializing boost::hash for pointers.
 

test/Jamfile.v2

@@ -43,6 +43,7 @@ test-suite container_hash/hash
         [ run hash_set_test.cpp ]
         [ run hash_map_test.cpp ]
         [ run hash_complex_test.cpp ]
+        [ run hash_optional_test.cpp ]
         [ run hash_type_index_test.cpp ]
         [ run hash_system_error_test.cpp ]
         [ run hash_std_array_test.cpp ]

test/hash_optional_test.cpp

@@ -0,0 +1,70 @@
+
+// Copyright 2018 Daniel James
+// 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)
+
+#include "./config.hpp"
+
+#ifndef BOOST_HASH_TEST_STD_INCLUDES
+#  include <boost/container_hash/hash.hpp>
+#endif
+#include <boost/config.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+#if BOOST_HASH_HAS_OPTIONAL
+
+#include <optional>
+#include <string>
+
+void test_optional_int()
+{
+    std::optional<int> x1a;
+    std::optional<int> x1b;
+    std::optional<int> x2a(10);
+    std::optional<int> x2b(x2a);
+    std::optional<int> x3(20);
+
+    boost::hash<std::optional<int> > hasher;
+
+    BOOST_TEST(hasher(x1a) == hasher(x1a));
+    BOOST_TEST(hasher(x1a) == hasher(x1b));
+    BOOST_TEST(hasher(x1a) != hasher(x2a));
+    BOOST_TEST(hasher(x1a) != hasher(x3));
+    BOOST_TEST(hasher(x2a) == hasher(x2a));
+    BOOST_TEST(hasher(x2b) == hasher(x2b));
+    BOOST_TEST(hasher(x2a) != hasher(x3));
+    BOOST_TEST(hasher(x3) == hasher(x3));
+}
+
+void test_optional_string()
+{
+    std::optional<std::string> x1a;
+    std::optional<std::string> x1b;
+    std::optional<std::string> x2a("10");
+    std::optional<std::string> x2b(x2a);
+    std::optional<std::string> x3("20");
+
+    boost::hash<std::optional<std::string> > hasher;
+
+    BOOST_TEST(hasher(x1a) == hasher(x1a));
+    BOOST_TEST(hasher(x1a) == hasher(x1b));
+    BOOST_TEST(hasher(x1a) != hasher(x2a));
+    BOOST_TEST(hasher(x1a) != hasher(x3));
+    BOOST_TEST(hasher(x2a) == hasher(x2a));
+    BOOST_TEST(hasher(x2b) == hasher(x2b));
+    BOOST_TEST(hasher(x2a) != hasher(x3));
+    BOOST_TEST(hasher(x3) == hasher(x3));
+}
+
+#endif
+
+int main()
+{
+#if BOOST_HASH_HAS_OPTIONAL
+    test_optional_int();
+    test_optional_string();
+#else
+    BOOST_LIGHTWEIGHT_TEST_OSTREAM << "<optional> not available." << std::endl;
+#endif
+    return boost::report_errors();
+}