Add macro to define has_member_xyz type trait.

SimoxUtility/CMakeLists.txt

@@ -53,6 +53,7 @@ SET(INCLUDES
     EigenStdVector.h
 
     meta/eigen/enable_if_compile_time_size.h
+    meta/has_member_macros/has_member.hpp
 
     algorithm/for_each_if.h
 

SimoxUtility/meta/has_member_macros/has_member.hpp

+// from: https://gist.github.com/maddouri/0da889b331d910f35e05ba3b7b9d869b
+
+// A compile-time method for checking the existence of a class member
+// @see https://general-purpose.io/2017/03/10/checking-the-existence-of-a-cpp-class-member-at-compile-time/
+
+// This code uses "decltype" which, according to http://en.cppreference.com/w/cpp/compiler_support
+// should be supported by Clang 2.9+, GCC 4.3+ and MSVC 2010+ (if you have an older compiler, please upgrade :)
+// As of "constexpr", if not supported by your compiler, you could try "const"
+// or use the value as an inner enum value e.g. enum { value = ... }
+
+// check "test_has_member.cpp" for a usage example
+
+/// Defines a "has_member_member_name" class template
+///
+/// This template can be used to check if its "T" argument
+/// has a data or function member called "member_name"
+#define define_has_member(member_name)                                         \
+    template <typename T>                                                      \
+    class has_member_##member_name                                             \
+    {                                                                          \
+        typedef char yes_type;                                                 \
+        typedef long no_type;                                                  \
+        template <typename U> static yes_type test(decltype(&U::member_name)); \
+        template <typename U> static no_type  test(...);                       \
+    public:                                                                    \
+        static constexpr bool value = sizeof(test<T>(0)) == sizeof(yes_type);  \
+    }
+
+/// Shorthand for testing if "class_" has a member called "member_name"
+///
+/// @note "define_has_member(member_name)" must be used
+///       before calling "has_member(class_, member_name)"
+#define has_member(class_, member_name)  has_member_##member_name<class_>::value
+