Merge pull request #61 from leapmotion/bug-errmsg

Adding more descriptive static assertions to AutoFilter

autowiring/has_autofilter.h

@@ -10,13 +10,15 @@
 template<class W, class Selector>
 struct has_valid_autofilter {
   // Evaluates to false for W::AutoFilter(void), else to true.
-  static const bool value = Decompose<decltype(&W::AutoFilter)>::N != 0;
+	static const int N = Decompose<decltype(&W::AutoFilter)>::N;
+	static const bool value = Decompose<decltype(&W::AutoFilter)>::N != 0;
 };
 
 // Specialization pertains only when W has no AutoFilter method.
 template<class W>
 struct has_valid_autofilter<W, std::false_type> {
-  static const bool value = false;
+	static const int N = -1;
+	static const bool value = false;
 };
 
 //===========================================================
@@ -43,8 +45,11 @@ struct has_unambiguous_autofilter
   template<class U>
   static std::true_type select(unnamed_constant<decltype(&U::AutoFilter), &U::AutoFilter>*);
 
+	// Conveninece typedef used externally:
+	typedef has_valid_autofilter<T, decltype(select<T>(nullptr))> has_valid;
+
   // Evaluates to true only if T includes a unique AutoFilter method with at least one argument.
-  static const bool value = has_valid_autofilter<T, decltype(select<T>(nullptr))>::value;
+	static const bool value = has_valid::value;
 };
 
 class AutoPacket;
@@ -66,10 +71,15 @@ struct has_autofilter {
   static const bool value = has_unambiguous_autofilter<T>::value;
 
   // This class has at least one AutoFilter method
-  struct detect_ambiguous_autofilter : T, test_valid_autofilter {};
+	struct detect_ambiguous_autofilter: T, test_valid_autofilter {};
+
+	// Validate the case most likely to have problems
+	static_assert(has_unambiguous_autofilter<T>::has_valid::N != 0, "Cannot define AutoFilter(void), your AutoFilter routine must take at least one argument");
 
   // Ensures a compiler error when the identification of T::AutoFilter is ambiguous.
   // This cannot be in has_unambiguous_autofilter, since that would be recursive.
-  static_assert(value || has_unambiguous_autofilter<detect_ambiguous_autofilter>::value,
-                "Cannot define more than 1 AutoFilter method. Cannot define AutoFilter(void)");
+  static_assert(
+		value || has_unambiguous_autofilter<detect_ambiguous_autofilter>::value,
+		"Cannot define more than one AutoFilter method and all AutoFilter methods must be public"
+	);
 };

src/autowiring/test/AutoFilterTest.cpp

@@ -469,7 +469,6 @@ TEST_F(AutoFilterTest, VerifyAntiDecorate) {
 /// </summary>
 template<typename T>
 struct good_autofilter {
-
   // Evaluates to false when T does not include an AutoFilter method with at least one argument.
   static const bool value = has_unambiguous_autofilter<T>::value;