Report notes for issue #1

Author: vinniefalco

Subtrees/beast/notes/1/test.cpp

@@ -0,0 +1,94 @@
+/*
+    This code normally fails to compile under Visual Studio 2012
+
+    The fix is marked with _MSC_VER
+*/
+
+#include <iostream>
+#include <typeinfo>
+
+template <class T> struct has_lowest_layer_type {
+  typedef char yes; 
+  typedef struct {char dummy[2];} no; 
+  template <class C> static yes f(typename C::lowest_layer_type*); 
+  template <class C> static no f(...); 
+#ifdef _MSC_VER
+  static const bool value = sizeof(f<T>(0)) == 1;
+#else
+  static const bool value = sizeof(has_lowest_layer_type<T>::f<T>(0)) == 1;
+#endif
+}; 
+
+template <bool Enable>
+struct EnableIf : std::false_type { };
+
+template <>
+struct EnableIf <true> : std::true_type { };
+
+struct tcp { };
+
+template <class Protocol>
+struct basic_socket
+{
+    typedef basic_socket <Protocol> lowest_layer_type;
+};
+
+template <class Protocol>
+struct basic_stream_socket : basic_socket <Protocol>
+{
+    typedef basic_socket <Protocol> next_layer_type;
+};
+
+struct A
+{
+    typedef basic_socket <tcp> lowest_layer_type;
+};
+
+struct B
+{
+};
+
+template <typename T>
+void show (std::true_type)
+{
+      std::cout << typeid(T).name() << " has lowest_layer_type" << std::endl;
+}
+ 
+template <typename T>
+void show (std::false_type)
+{
+      std::cout << typeid(T).name() << " does not have lowest_layer_type" << std::endl;
+}
+ 
+template <typename T>
+void show ()
+{
+  show <T> (EnableIf <has_lowest_layer_type <T>::value> ());
+}
+ 
+int main ()
+{
+  show <A> ();
+  show <B> ();
+  show <basic_socket <tcp> > ();
+  show <basic_stream_socket <tcp> > ();
+  return 0;
+}
+/*
+1>..\..\Subtrees\beast\notes\1\test.cpp(16): error C2783: 'has_lowest_layer_type<T>::no has_lowest_layer_type<T>::f(...)' : could not deduce template argument for 'C'
+1>          with
+1>          [
+1>              T=A
+1>          ]
+1>          ..\..\Subtrees\beast\notes\1\test.cpp(15) : see declaration of 'has_lowest_layer_type<T>::f'
+1>          with
+1>          [
+1>              T=A
+1>          ]
+1>          ..\..\Subtrees\beast\notes\1\test.cpp(63) : see reference to class template instantiation 'has_lowest_layer_type<T>' being compiled
+1>          with
+1>          [
+1>              T=A
+1>          ]
+1>          ..\..\Subtrees\beast\notes\1\test.cpp(68) : see reference to function template instantiation 'void show<A>(void)' being compiled
+*/