Introducing ReturnValue

The objective of ReturnValue is to maintain coherency with ErrorCode
class in cases where a single value is used to represent both the error
and the return value

api/ErrorCodes.h

@@ -27,5 +27,37 @@ class ErrorCode {
     }
 };
 
+/* ReturnValueClass is meant to represent all the cases where with a single value
+ * we want to return an error, if the value is negative, or a meaningful result
+ * if greater than or equal to 0.
+ * In order to be retrocompatible with the previous definition boolean evaluation:
+ * - It must return true, if the value is greater than or equal 0
+ * - It must return false, if the value is negatie
+ * - It must be evaluable as the primitive type associated with
+ */
+template<typename T>
+class ReturnValueClass {
+public:
+    constexpr ReturnValueClass(T value)
+    : value(value >= 0? value : 0), error(value < 0? (error_t)value : ArduinoSuccess) {}
+
+    // it would be nice to have a default value on error to Success
+    constexpr ReturnValueClass(T value, error_t error)
+    : value(value), error(error) {}
+
+    const T value; // TODO should we leave the const modifier?
+    const error_t error;
+
+    constexpr operator bool() const {
+        return error == ArduinoSuccess;
+    }
+
+    constexpr operator T() const {
+        return error == ArduinoSuccess ? value : error;
+    }
+};
+
+using ReturnValue       = ReturnValueClass<int>;
+using ReturnLongValue   = ReturnValueClass<int64_t>;
 
 }