Made the compile time assert macros use static_assert if it's available.

dlib/assert.h

@@ -26,6 +26,20 @@
 #define BOOST_DO_JOIN2( X, Y ) X##Y
 #endif
 
+// figure out if the compiler has static_assert. 
+#if defined(__clang__) 
+#   if __has_feature(cxx_static_assert)
+#       define DLIB_HAS_STATIC_ASSERT
+#   endif
+#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2)) && defined(__GXX_EXPERIMENTAL_CXX0X__) 
+#   define DLIB_HAS_STATIC_ASSERT
+#elif defined(_MSC_VER) && _MSC_VER >= 1600
+#   define DLIB_HAS_STATIC_ASSERT
+#elif defined(__INTEL_COMPILER) && defined(BOOST_INTEL_STDCXX0X)
+#   define DLIB_HAS_STATIC_ASSERT
+#endif
+
+
 // -----------------------------
 
 namespace dlib
@@ -37,6 +51,9 @@ namespace dlib
     template <typename T> struct assert_are_same_type<T,T> {enum{value=1};};
     template <typename T, typename U> struct assert_are_not_same_type {enum{value=1}; };
     template <typename T> struct assert_are_not_same_type<T,T> {};
+
+    template <typename T, typename U> struct assert_types_match {enum{value=0};};
+    template <typename T> struct assert_types_match<T,T> {enum{value=1};};
 }
 
 
@@ -48,14 +65,22 @@ namespace dlib
 #define DLIB_NO_WARN_UNUSED 
 #endif
 
-#define COMPILE_TIME_ASSERT(expression) \
+// Use the newer static_assert if it's avaiable since it produces much more readable error
+// messages.
+#ifdef DLIB_HAS_STATIC_ASSERT
+    #define COMPILE_TIME_ASSERT(expression) static_assert(expression, "Failed assertion")
+    #define ASSERT_ARE_SAME_TYPE(type1, type2) static_assert(assert_types_match<type1,type2>::value, "These types should be the same but aren't.")
+    #define ASSERT_ARE_NOT_SAME_TYPE(type1, type2) static_assert(!assert_types_match<type1,type2>::value, "These types should NOT be the same.")
+#else
+    #define COMPILE_TIME_ASSERT(expression) \
         DLIB_NO_WARN_UNUSED typedef char BOOST_JOIN(DLIB_CTA, __LINE__)[::dlib::compile_time_assert<(bool)(expression)>::value] 
 
-#define ASSERT_ARE_SAME_TYPE(type1, type2) \
+    #define ASSERT_ARE_SAME_TYPE(type1, type2) \
         DLIB_NO_WARN_UNUSED typedef char BOOST_JOIN(DLIB_AAST, __LINE__)[::dlib::assert_are_same_type<type1,type2>::value] 
 
-#define ASSERT_ARE_NOT_SAME_TYPE(type1, type2) \
+    #define ASSERT_ARE_NOT_SAME_TYPE(type1, type2) \
         DLIB_NO_WARN_UNUSED typedef char BOOST_JOIN(DLIB_AANST, __LINE__)[::dlib::assert_are_not_same_type<type1,type2>::value] 
+#endif
 
 // -----------------------------