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POBoost Statechart - Local transitions
 

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    <p>I'm hoping that someone can help me out with this problem, or at least point out the error of my ways... </p> <p>As a simple illustration of my problem consider a part of an application where you can enter a "Functions Mode" state of operation. Four sub-modes are then available depending on which function key F1-F4 that the user presses. By default, F1 mode is entered. The state diagram starts off as follows: </p> <p><img src="https://i.stack.imgur.com/VI05u.png" alt="Diagram 1"></p> <p>The user can press F1-F4 at any time to switch to the corresponding mode. Adding these transitions to the inner states leads to the following:</p> <p><img src="https://i.stack.imgur.com/SeR05.png" alt="Diagram 2"></p> <p>Obviously this is (a) a mess, and (b) a lot of transitions to define. If at some point I want to add an F5Mode then... well, you get the picture. To avoid this I'd like to do the following:</p> <p><img src="https://i.stack.imgur.com/itPhV.png" alt="Diagram 3"></p> <p>Boost Statechart allows me to define transitions from FunctionMode to any of the inner states, but the result isn't what I expected. The actual outcome is as follows:</p> <p><img src="https://i.stack.imgur.com/NgGGh.png" alt="Diagram 4"></p> <p>I.e. pressing F1-F4 to switch modes causes the outer FunctionMode state to be exited and re-entered along with triggering the unwanted exit and entry actions.</p> <p>Way back in 2006, <a href="http://boost.2283326.n4.nabble.com/statechart-UML2-0-local-transitions-and-history-td2557450.html" rel="nofollow noreferrer">this thread</a> between the library author and a user seems to describe the same problem. I think that the author suggests doing the following as a work-around:</p> <p><img src="https://i.stack.imgur.com/BVRjR.png" alt="Diagram 5"> </p> <p>However, that work-around doesn't seem very appealing to me: It has added an extra state level to be compiled, the code has become less readable, deep-history would have to be used to return to any of the function mode sub-states and the Intermediate state object is needlessly being destructed and constructed again.</p> <p>So... where am I going wrong? Or what are the alternatives? I've had a brief look at Boost Meta State Machine (msm) but from what I've seen so far I much prefer the look of Statechart.</p> <p>I'm surprised that more users haven't faced the same problem... which makes me think that perhaps my approach is completely wrong!</p>
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