Mechanism for better compile-time error messages

src/libraries/JANA/Utils/JTypeInfo.h

@@ -12,6 +12,20 @@
 
 namespace JTypeInfo {
 
+
+template <typename, typename=void>
+struct is_parseable : std::false_type {};
+
+template <typename T>
+struct is_parseable<T, std::void_t<decltype(std::declval<std::istream>() >> std::declval<T&>())>> : std::true_type {};
+
+template <typename, typename=void>
+struct is_serializable : std::false_type {};
+
+template <typename T>
+struct is_serializable<T, std::void_t<decltype(std::declval<std::ostream>() << std::declval<T>())>> : std::true_type {};
+
+
 template<typename T>
 std::string demangle(void) {
 

src/programs/tests/JParameterManagerTests.cc

@@ -402,4 +402,35 @@ TEST_CASE("JParameterManager_Issue217StringsWithWhitespace") {
     }
 }
 
+#if __cplusplus >= 201703L
+template <typename T>
+void fakeParse(std::string s, T& out) {
+    constexpr bool parseable = JTypeInfo::is_parseable<T>::value;
+    static_assert(parseable, "Type is not automatically supported by the ParameterManager. To use, implement a template specialization for Parse(std::string in, T& out).");
+    if constexpr (parseable) {
+        std::stringstream ss;
+        ss >> out;
+    }
+}
+#else
+template <typename T>
+void fakeParse(std::string s, T& out) {
+    std::stringstream ss;
+    ss >> out;
+}
+#endif
+}
+
+
+enum class Mood {Good, Bad, Mediocre};
+TEST_CASE("Error message on bad parse") {
+    int x;
+    fakeParse("22", x);
+    Mood m;
+    fakeParse("Mediocre", m);
+}
+
+
+
+