Make common_type SFINAE-friendly, add tests

test/common_type_6_test.cpp

@@ -0,0 +1,39 @@
+
+//  Copyright Peter Dimov 2015
+//  Use, modification and distribution are subject to the 
+//  Boost Software License, Version 1.0. (See accompanying file 
+//  LICENSE_1_0.txt or copy at http://www.tt.org/LICENSE_1_0.txt)
+
+#include "test.hpp"
+#include "check_type.hpp"
+#ifdef TEST_STD
+#  include <type_traits>
+#else
+#  include <boost/type_traits/common_type.hpp>
+#endif
+#include <iostream>
+
+struct X {};
+struct Y: X {};
+
+TT_TEST_BEGIN(common_type_6)
+{
+    // binary case
+
+    BOOST_CHECK_TYPE3(tt::common_type<void, void>::type, void);
+
+    BOOST_CHECK_TYPE3(tt::common_type<int, int>::type, int);
+    BOOST_CHECK_TYPE3(tt::common_type<int&, int&>::type, int);
+    BOOST_CHECK_TYPE3(tt::common_type<int&, int const&>::type, int);
+
+    BOOST_CHECK_TYPE3(tt::common_type<X, X>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X&, X&>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X&, X const&>::type, X);
+
+    BOOST_CHECK_TYPE3(tt::common_type<X, Y>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X&, Y&>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X const&, Y&>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X&, Y const&>::type, X);
+    BOOST_CHECK_TYPE3(tt::common_type<X const&, Y const&>::type, X);
+}
+TT_TEST_END

test/common_type_sfinae2_test.cpp

@@ -0,0 +1,39 @@
+
+//  Copyright Peter Dimov 2015
+//  Use, modification and distribution are subject to the 
+//  Boost Software License, Version 1.0. (See accompanying file 
+//  LICENSE_1_0.txt or copy at http://www.tt.org/LICENSE_1_0.txt)
+
+#include "test.hpp"
+#include "check_integral_constant.hpp"
+#ifdef TEST_STD
+#  include <type_traits>
+#else
+#  include <boost/type_traits/common_type.hpp>
+#  include <boost/type_traits/integral_constant.hpp>
+#endif
+#include <iostream>
+
+typedef char(&s1)[1];
+typedef char(&s2)[2];
+
+template<class T> s1 has_type_impl( typename T::type * );
+template<class T> s2 has_type_impl( ... );
+
+template<class T> struct has_type: tt::integral_constant<bool, sizeof(has_type_impl<T>(0)) == sizeof(s1)> {};
+
+struct X {};
+struct Y {};
+
+TT_TEST_BEGIN(common_type_sfinae2)
+{
+#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+
+    BOOST_CHECK_INTEGRAL_CONSTANT( (has_type< tt::common_type<int, void*> >::value), false );
+    BOOST_CHECK_INTEGRAL_CONSTANT( (has_type< tt::common_type<X, Y> >::value), false );
+    BOOST_CHECK_INTEGRAL_CONSTANT( (has_type< tt::common_type<X&, int const*> >::value), false );
+    BOOST_CHECK_INTEGRAL_CONSTANT( (has_type< tt::common_type<X, Y, int, void*> >::value), false );
+
+#endif
+}
+TT_TEST_END

test/common_type_sfinae_test.cpp

@@ -0,0 +1,45 @@
+
+//  Copyright Peter Dimov 2015
+//  Use, modification and distribution are subject to the 
+//  Boost Software License, Version 1.0. (See accompanying file 
+//  LICENSE_1_0.txt or copy at http://www.tt.org/LICENSE_1_0.txt)
+
+#include "test.hpp"
+#include "check_type.hpp"
+#ifdef TEST_STD
+#  include <type_traits>
+#else
+#  include <boost/type_traits/common_type.hpp>
+#endif
+#include <iostream>
+
+struct X {};
+struct Y {};
+
+TT_TEST_BEGIN(common_type_sfinae)
+{
+#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+
+    {
+        tt::common_type<int, void*> tmp;
+        (void)tmp;
+    }
+
+    {
+        tt::common_type<X, Y> tmp;
+        (void)tmp;
+    }
+
+    {
+        tt::common_type<X&, int const*> tmp;
+        (void)tmp;
+    }
+
+    {
+        tt::common_type<X, Y, int, void*> tmp;
+        (void)tmp;
+    }
+
+#endif
+}
+TT_TEST_END