C/C++: parameters enqueueing as pointers should be deprecated

[vassik]

Following discussion with Franck, we should deprecate enqueueing of a message parameter as a pointer to this parameter. Even though it can work when the parameter is allocated in the heap (e.g. the ThingML String type is generated as char*) and things are run on the same machine.

Moreover, ports and messages are concepts which may be used to communicate between things on different machines; thus, a pointer does not make sense.

In addition, please consider the following erroneous example in ThingML:

thing fragment Messages {
    message send_bytes(mbytes : Byte[32]);
}

thing Sender includes Messages {
....
        state SBytes {
            on entry do
                var data : Byte[32]
                data[0] = '0'
                data[1] = '1' 
                datasender!send_bytes(data)
            end         
....
        }

and generated code for the 'on entry' block in C

void Sender_send_datasender_send_bytes(struct Sender_Instance *_instance, uint8_t* mbytes);

void Sender_Behavior_OnEntry(int state, struct Sender_Instance *_instance) {
...
case SENDER_BEHAVIOR_SBYTES_STATE:
{
uint8_t data[32];
data[0] = '0';
data[1] = '1';
cout << "Send bytes "<<data[0]<< data[1] << endl;
Sender_send_datasender_send_bytes(_instance, data);
}
break;
...
}

Since the message handling happens asynchronously, and we pass a pointer to a value (mbytes) on the stack, the pointer contents is changed.