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Content-type: text/plain
Gerard and Robert:
I want to say I am impressed with the Wrapper that Gerard has sent
to the list. I would have never guessed such things are possible.
I am not a computer scientist and this level of trickery is
entirely above me. Anyway, I am still in the dark concerning
how to store Dialogs to disk. Dan who works with me on this project
has defined a "wrapper" type like this
TYPE
MyTree* = POINTER TO RECORD (Stores.Store)
tree*:Dialog.Tree
END;
But now what? He still needs to write the entire Internalize/
Externalize, which means traversing the tree and storing the
whole structure to disk. Basically, he needs to build an entire
"shadow tree" in memory, whose only purpose is that it can
be written to disk. The reverse needs to be done when reading
back. This looks like a lot of busy work to me.
Gerard has made a neat example, but his Wrapper wraps a View
which is persistent, and thus it will know how to write itself
to disk. But Dialog is NOT persistent, and hence it will not
store itself. Now we have to recreate the tree by hand when
writing/reading, just for the purpose of writing it to disk.
The point is made even more glaring by Robert saying he "extended"
the FormModel by adding his own pointer, what was possible
because the Form *source* is available. This is not the kind
of extension we were taught by Ominc, are we? But when
even such an expert like Robert has to resort to the source,
then I am even more thrown off into the dark.
Am I missing something obvious here? Is there an smart trick
to write a dialog to disk, or do we have to do everything
by hand from scratch, without even resorting to Robert's
method because this time no source is available?
Thank you,
Wojtek Skulski skulski{([at]})nowhere.xy
> > Wojtek Skulski skulski{([at]})nowhere.xy
>
> > In particular, we are not sure how we can implement
> > Internalize/Externalize for objects which are not
> > persistent.
> >
>Robert wrote:
>
> I have some 'Calculator' Forms which I wanted to save complete
> with the numbers in the Field Controls. Since the source of the
> Form SubSystem is public I extended FormModels.Model to include
> a variable myPtr* : Stores.Store. By assigning the 'Calculator'
> data to myPtr its Externalize (etc) routine is called when the form
> is Saved/Copied.
>
> I use FormModels.SetDir to enable my forms, which are then provided
> by the usual Menu item Controls->New Form.
> Gerard Meunier wrote:
> I have another solution, using wrappers. You can find examples in Obx, Pac,
> Plot, TabMult, etc... It's the way Wirth made complex objects in Oberon, and
> it works too in BB. It uses object composition instead of inheritance
> (Szyperski 1999, Component Software) and works even if the source code is
> unavailable.
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Received on Fri Jun 27 2003 - 05:31:09 UTC