Non-functioning solution

This would have been so convenient, but alas C++ doesn't allow us to convert
from lambdas to function pointers.

Error we get:
Core/ClientSML/src/sml_ClientKernel.cpp:2225:45: error: no viable conversion from '(lambda at Core/ClientSML/src/sml_ClientKernel.cpp:2194:23)' to 'sml::RhsEventHandler' (aka 'const char *(*)(sml::smlRhsEventId, void *, sml::Agent *, const char *, const char *, int *, char *)')
    return AddRhsFunction(pRhsFunctionName, newHandler, pUserData, addToBack);
                                            ^~~~~~~~~~
Core/ClientSML/src/sml_ClientKernel.cpp:2185:74: note: passing argument to parameter 'handler' here
int Kernel::AddRhsFunction(char const* pRhsFunctionName, RhsEventHandler handler, void* pUserData, bool addToBack)
                                                                         ^
1 error generated.

See
https://stackoverflow.com/questions/28746744/passing-capturing-lambda-as-function-pointer.

Core/ClientSML/src/sml_ClientEvents.h

@@ -100,13 +100,16 @@ namespace sml
     typedef char const *(*RhsEventHandler)(smlRhsEventId id, void* pUserData, Agent* pAgent,
                                           char const* pFunctionName, char const* pArgument, int *buffSize, char *buff) ;
 
+    typedef std::string(*RhsEventHandlerManaged)(smlRhsEventId id, void* pUserData, Agent* pAgent,
+                                          char const* pFunctionName, char const* pArgument) ;
 // Handler for a generic "client message".  The content is determined by the client sending this data.
 // The message is sent as a simple string and the response is also a string.  The string can contain data that is intended to be parsed,
 // such as a simple series of integers up to a complete XML message.
 // SEE MAINTAINER NOTE ABOVE!
 		typedef char const *(*ClientMessageHandler)(smlRhsEventId id, void* pUserData, Agent* pAgent,
 																					 char const* pFunctionName, char const* pArgument, int *buffSize, char *buff) ;
-
+        typedef std::string(*ClientMessageHandlerManaged)(smlRhsEventId id, void* pUserData, Agent* pAgent,
+            char const* pClientName, char const* pMessage) ;
 // We'll store a handler function together with a generic pointer to data of the user's choosing
 // (which is then passed back into the handler when the event occurs).
 // We also include a callback "id" which is a unique way to refer to this callback--used during unregistering.

Core/ClientSML/src/sml_ClientKernel.cpp

@@ -2189,6 +2189,42 @@ int Kernel::AddRhsFunction(char const* pRhsFunctionName, RhsEventHandler handler
     return InternalAddRhsFunction(id, pRhsFunctionName, handler, pUserData, addToBack) ;
 }
 
+int Kernel::AddRhsFunctionManaged(char const* pRhsFunctionName, RhsEventHandlerManaged handler, void* pUserData, bool addToBack)
+{
+    auto newHandler = [&handler](
+        smlRhsEventId id,
+        void* pUserData,
+        Agent* pAgent,
+        char const* pFunctionName,
+        char const* pArgument,
+        int *bufSize,
+        char *buf) -> char * {
+            static std::string prevResult;
+            // Previous call could not return the full result and cached it in prevResult instead.
+            // Return the cached result and clear the cache.
+            if ( !prevResult.empty() )
+            {
+                strncpy( buf, prevResult.c_str(), *bufSize );
+                prevResult = "";
+                return buf;
+            }
+
+            std::string resultStr = handler(id, pUserData, pAgent, pFunctionName, pArgument);
+            // Result won't fit in the buffer. Return NULL and set buffSize to the required size.
+            // Soar will then re-call this handler and get the cached result.
+            if ( resultStr.length() + 1 > *bufSize )
+            {
+                *bufSize = resultStr.length() + 1;
+                prevResult = resultStr;
+                return NULL;
+            }
+
+            strcpy( buf, resultStr.c_str() );
+            return buf;
+        };
+    return AddRhsFunction(pRhsFunctionName, newHandler, pUserData, addToBack);
+}
+
 /*************************************************************
 * @brief Unregister for a particular RHS function
 *************************************************************/

Core/ClientSML/src/sml_ClientKernel.h

@@ -781,6 +781,7 @@ namespace sml
             * @returns Unique ID for this callback.  Required when unregistering this callback.
             *************************************************************/
             int AddRhsFunction(char const* pRhsFunctionName, RhsEventHandler handler, void* pUserData, bool addToBack = true) ;
+            int AddRhsFunctionManaged(char const* pRhsFunctionName, RhsEventHandlerManaged handler, void* pUserData, bool addToBack = true) ;
 
             /*************************************************************
             * @brief Unregister for a particular rhs function callback