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Subject: Re: [boost] [msm]omitting region id at the entry pseudo state
From: Christophe Henry (christophe.j.henry_at_[hidden])
Date: 2012-03-04 16:25:27

Hi Takatoshi,

> Hello,
> Now, I'm using Boost.Msm (Version1.49.0).
> I have a question about a transition behavior when I omit a region id
> at the entry pseudo state.
> The document said that when we use the explicit entry, if the state
> machine satisfied the conditions below, we can omit the region id.
> " Thanks to the mpl_graph library you can also omit to provide the
> region index and let MSM find out for you. The are however two points
> to note:
> - MSM can only find out the region index if the explicit entry state
> is somehow connected to an initial state through a transition, no
> matter the direction.
> - There is a compile-time cost for this feature. "
> Because of the discussion below, I believe that this rule can also be
> applied to entry pseudo states.

It does, I just forgot to mention it in the doc.

> However, when I omitted the region id, the state machine transitioned
> to the SubState1.
> struct Entry1:msmf::entry_pseudo_state<> {};
> If I provided the region id, the state machine transitioned to the
> SubState2.
> struct Entry1:msmf::entry_pseudo_state<0> {};
> See entry_pt_omit_rid.cpp (Attached file)
> As far as I can understand, Entry1 and SubState1, initial_state, are
> connected. (See fig.png)
> Is there any reason that I can't omit the region id in this case?

Looks like a bug. It's a bit late to fix it tonight, but if I change your
initial state declaration to:

typedef mpl::vector<SubState1> initial_state;

Then it works. Must be some silly mistake and not too hard to fix, but you
can use the workaround in the meantime.


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