[boost] Re: [prereview request][fsm]

From: David Abrahams (dave_at_[hidden])
Date: 2004-05-23 11:12:50

"Andreas Huber" <ah2003_at_[hidden]> writes:

>> That seems like a bad limitation, and for me it calls into question
>> the idea of mapping state exit to destructors.  Can you explain why
>> that's the right design?
>
> Yes, there's a lot of evidence that state exit actions must not fail:
>
> Say you have a state_machine<> subclass S and an object of that class, which
> currently resides in state A and state B nested in A (see the picture under
> Error handling in ratinale.html). Inside S::~S, the state machine is
> terminated what leads to the exit actions of B and A being executed. If B's
> exit action fails, what can you do with the resulting exception? I guess we
> agree that you cannot propagate it out of S::~S.

You miss my point.  I know destructors must not fail.  I am suggesting
that it may have been the wrong decision to represent state exit
actions with destructors; you could've used some other protocol.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com