Use boost::hash in hash_value, not std::hash (closes #27)

.travis.yml

@@ -1,4 +1,4 @@
-# Copyright 2016-2019 Peter Dimov
+# Copyright 2016-2021 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
@@ -165,6 +165,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-5.0
       env: TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=11,14,1z
       addons:
@@ -175,6 +176,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-6.0
       env: TOOLSET=clang COMPILER=clang++-6.0 CXXSTD=11,14,17
       addons:
@@ -185,6 +187,7 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
+      dist: bionic
       compiler: clang++-7
       env: TOOLSET=clang COMPILER=clang++-7 CXXSTD=11,14,17,2a
       addons:
@@ -193,9 +196,10 @@ matrix:
             - clang-7
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-7
+            - llvm-toolchain-bionic-7
 
     - os: linux
+      dist: bionic
       compiler: clang++-8
       env: TOOLSET=clang COMPILER=clang++-8 CXXSTD=11,14,17,2a
       addons:
@@ -204,10 +208,10 @@ matrix:
             - clang-8
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-8
+            - llvm-toolchain-bionic-8
 
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: clang++-9
       env: TOOLSET=clang COMPILER=clang++-9 CXXSTD=11,14,17,2a
       addons:
@@ -216,11 +220,11 @@ matrix:
             - clang-9
           sources:
             - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
               key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: clang++-10
       env: TOOLSET=clang COMPILER=clang++-10 CXXSTD=11,14,17,2a
       addons:
@@ -229,20 +233,33 @@ matrix:
             - clang-10
           sources:
             - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-10 main'
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-10 main'
               key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux
-      dist: xenial
+      dist: bionic
       compiler: clang++-11
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-11 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
+      env: TOOLSET=clang COMPILER=clang++-11 CXXSTD=11,14,17,2a
       addons:
         apt:
           packages:
             - clang-11
           sources:
             - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-11 main'
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-11 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
+
+    - os: linux
+      dist: bionic
+      compiler: clang++-12
+      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-12 CXXSTD=11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
+      addons:
+        apt:
+          packages:
+            - clang-12
+          sources:
+            - ubuntu-toolchain-r-test
+            - sourceline: 'deb https://apt.llvm.org/bionic/ llvm-toolchain-bionic-12 main'
               key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux

include/boost/variant2/variant.hpp

@@ -26,6 +26,7 @@
 #include <initializer_list>
 #include <utility>
 #include <functional> // std::hash
+#include <cstdint>
 
 //
 
@@ -38,6 +39,8 @@ BOOST_NORETURN void throw_exception( std::exception const & e ); // user defined
 
 #endif
 
+template<class T> struct hash;
+
 namespace variant2
 {
 
@@ -2195,31 +2198,59 @@ void swap( variant<T...> & v, variant<T...> & w )
 namespace detail
 {
 
-template<class V> struct hash_value_L
+inline std::size_t hash_value_impl_( mp11::mp_true, std::size_t index, std::size_t value )
+{
+    boost::ulong_long_type hv = ( boost::ulong_long_type( 0xCBF29CE4 ) << 32 ) + 0x84222325;
+    boost::ulong_long_type const prime = ( boost::ulong_long_type( 0x00000100 ) << 32 ) + 0x000001B3;
+
+    hv ^= index;
+    hv *= prime;
+
+    hv ^= value;
+    hv *= prime;
+
+    return static_cast<std::size_t>( hv );
+}
+
+inline std::size_t hash_value_impl_( mp11::mp_false, std::size_t index, std::size_t value )
+{
+    std::size_t hv = 0x811C9DC5;
+    std::size_t const prime = 0x01000193;
+
+    hv ^= index;
+    hv *= prime;
+
+    hv ^= value;
+    hv *= prime;
+
+    return hv;
+}
+
+inline std::size_t hash_value_impl( std::size_t index, std::size_t value )
+{
+    return hash_value_impl_( mp11::mp_bool< (SIZE_MAX > UINT32_MAX) >(), index, value );
+}
+
+template<template<class> class H, class V> struct hash_value_L
 {
     V const & v;
 
     template<class I> std::size_t operator()( I ) const
     {
-        boost::ulong_long_type hv = ( boost::ulong_long_type( 0xCBF29CE4 ) << 32 ) + 0x84222325;
-        boost::ulong_long_type const prime = ( boost::ulong_long_type( 0x00000100 ) << 32 ) + 0x000001B3;
-
-        // index
-
-        hv ^= I::value;
-        hv *= prime;
-
-        // value
-
         auto const & t = unsafe_get<I::value>( v );
 
-        hv ^= std::hash<remove_cv_ref_t<decltype(t)>>()( t );
-        hv *= prime;
+        std::size_t index = I::value;
+        std::size_t value = H<remove_cv_ref_t<decltype(t)>>()( t );
 
-        return static_cast<std::size_t>( hv );
+        return hash_value_impl( index, value );
     }
 };
 
+template<class... T> std::size_t hash_value_std( variant<T...> const & v )
+{
+    return mp11::mp_with_index<sizeof...(T)>( v.index(), detail::hash_value_L< std::hash, variant<T...> >{ v } );
+}
+
 } // namespace detail
 
 inline std::size_t hash_value( monostate const & )
@@ -2229,7 +2260,7 @@ inline std::size_t hash_value( monostate const & )
 
 template<class... T> std::size_t hash_value( variant<T...> const & v )
 {
-    return mp11::mp_with_index<sizeof...(T)>( v.index(), detail::hash_value_L< variant<T...> >{ v } );
+    return mp11::mp_with_index<sizeof...(T)>( v.index(), detail::hash_value_L< boost::hash, variant<T...> >{ v } );
 }
 
 namespace detail
@@ -2250,7 +2281,7 @@ template<class V> struct std_hash_impl<V, true>
 {
     std::size_t operator()( V const & v ) const
     {
-        return hash_value( v );
+        return detail::hash_value_std( v );
     }
 };
 

test/variant_hash.cpp

@@ -12,6 +12,7 @@
 #include <boost/core/lightweight_test_trait.hpp>
 #include <boost/container_hash/hash.hpp>
 #include <boost/config/workaround.hpp>
+#include <vector>
 
 using namespace boost::variant2;
 
@@ -47,7 +48,17 @@ template<template<class...> class Hash, class T> void test2()
     BOOST_TEST_NE( h2, h3 );
 }
 
-struct X {};
+struct X
+{
+    int m = 0;
+};
+
+std::size_t hash_value( X const& x )
+{
+    return boost::hash<int>()( x.m );
+}
+
+struct Y {}; // no hash support
 
 int main()
 {
@@ -57,6 +68,8 @@ int main()
     test<boost::hash, monostate, monostate, monostate>();
     test<boost::hash, int, int, float>();
 
+    test<boost::hash, monostate, X, std::vector<X>>();
+
     test2<std::hash, int>();
     test2<std::hash, float>();
 
@@ -65,7 +78,7 @@ int main()
 
 #if !BOOST_WORKAROUND(BOOST_MSVC, < 1910) && ( !defined(_LIBCPP_STD_VER) || _LIBCPP_STD_VER > 11 )
 
-    BOOST_TEST_TRAIT_FALSE(( detail::is_hash_enabled<X> ));
+    BOOST_TEST_TRAIT_FALSE(( detail::is_hash_enabled<Y> ));
 
 #endif