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I have a problem with the sequence model seen in the diagram below, specifically where the System object is creating a new Number. In this case, there is no need for a return message since the function SaveInput(n), both in System and Number, is the end of the line for that portion of the program, but unless I include one, the modeller reshaped my diagram into the other one I've uploaded here, and I can't see how to arrange the messages so that my program will work the way I intend without including the return message (the one without a name) from Number to System, since the functions SaveInput() both return a void.

How should void-returning functions be handled in sequence diagrams so that they behave correctly? I have opened the message properties and explicitly defined it as returning a void, but that hasn't helped.

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    Don't understand why Return subtracted value bypasses the system. On the void thingy: void is just a value, you handle and model it just like you would return a boolen or errorcode or any other object for that matter. That a method returns void doesn't mean 'fire-and-forget' – rene Feb 14 '11 at 20:17

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When A calls operation b in B, the "return" arrow from B to A indicates the end of the operation b has finished its execution. This doesn´t mean that as part of the return message you have to return a value, it only means that the execution is done and you can continue with the next messages. Visually, most tools also use these return messages to manage the life bar of the object.

Jordi Cabot
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