Add example/hash_without_seed.cpp

example/Jamfile

@@ -7,3 +7,4 @@ exe md5sum : md5sum.cpp ;
 exe hash2sum : hash2sum.cpp ;
 exe compile_time : compile_time.cpp ;
 exe compile_time_2 : compile_time_2.cpp ;
+exe hash_without_seed : hash_without_seed.cpp ;

example/hash_without_seed.cpp

@@ -0,0 +1,29 @@
+// Copyright 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/hash2/siphash.hpp>
+#include <boost/hash2/hash_append.hpp>
+#include <boost/hash2/get_integral_result.hpp>
+#include <boost/unordered/unordered_flat_map.hpp>
+#include <string>
+
+template<class T, class H> class hash
+{
+public:
+
+    std::size_t operator()( T const& v ) const
+    {
+        H h;
+        boost::hash2::hash_append( h, {}, v );
+        return boost::hash2::get_integral_result<std::size_t>( h.result() );
+    }
+};
+
+int main()
+{
+    boost::unordered_flat_map<std::string, int, hash<std::string, boost::hash2::siphash_64>> map;
+
+    map[ "foo" ] = 1;
+    map[ "bar" ] = 2;
+}

test/Jamfile

@@ -165,3 +165,4 @@ link ../example/md5sum.cpp ;
 link ../example/hash2sum.cpp : <cxxstd>11:<build>no <toolset>msvc-14.0:<build>no ;
 link ../example/compile_time.cpp : <cxxstd>11:<build>no <toolset>msvc-14.0:<build>no ;
 link ../example/compile_time_2.cpp : <cxxstd>11:<build>no <toolset>msvc-14.0:<build>no <toolset>gcc-5:<build>no ;
+link ../example/hash_without_seed.cpp ;