Subject: Re: [boost] [MSM] Is there any interest in C++14 Boost.MSM-eUML like library which compiles up to 60x quicker whilst being a slightly faster too?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2016-02-15 07:17:24
Le 15/02/2016 11:08, Krzysztof Jusiak a écrit :
> On Fri, Feb 12, 2016 at 6:44 PM, Vicente J. Botet Escriba <
> vicente.botet_at_[hidden]> wrote:
>
>> Le 12/02/2016 12:20, Krzysztof Jusiak a écrit :
>>
>
> For me it is semi clear, but I do agree with your conclusion though.
> However, there is no info about guards being executed before src state exit.
> It might be implied by the statement that transition has to be enabled, but
> I'm not sure about it.
>
Yes, I believe that event reception and the guard evaluation are the enablers of the transition.
>>
>> BTW. I have a question related to local transitions. Concept seems to be
>>>>> nice but I don't undesrtand why exit/entry is NOT triggered only 'if the
>>>>> main target state is a substate of the main source'.
>>>>> Why this concept can't be more general? Wouldn't that be nice?
>>>>>
>>>>> s1 + e1 = s2 // exit from s1 / entry to s2
>>>>> s1 ^ e1 = s2 // no exit from s1 / no entry to s2
>>>>>
>>>>>
>>>>> A local transition will ensure that there is no exit on s1, but there
>>>>>
>>>> should be an entry in s2 if s2 is not s1.
>>>> You will need to have a nested examples to see the difference between an
>>>> external and a local transition.
>>>>
>>> Yea, I do get it. Cheers. Do have any example when local transitions are
>>> useful? I see some usage for them but I struggle really to find a really
>>> good use case for them.
>>>
>>>
>>>
>>> Let say that you have a state S with two sub-states S1 and S2.
>> While in state S, if you receive the event E1 you want to go to S1, but
>> don't want to execute the exit of state S. However you want to execute the
>> exit of S1 or S2.
>>
>> S ^ E1 = S1;
>>
>> Think of E1 as an event that interrupts whatever you were doing on S1 or
>> S2.
>>
>>
> Yea, yea I do get that. I was asking more about real life example. I mean,
> what use case would require such behavior, because I can't think of any,
> but I know there are some.
> I'm asking because I don't have any experience with local transition and it
> is hard to justify adding a new feature without a meaningful rationale.
>
>
Let say that we are on a disabled state. In this state you have
sub-states representing the path to go to another enabled state (e.g.
requesting a password, ...) .
If you receive a reset event this would disable any trial to go to the
enabled state.
From the disabled state you could have a local transition when
receiving this reset event and go to the sub-state disabled/idle.
What is important is that you are always in the disabled state, so the
disabled exit has not been executed.
Vicente