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st: Dialog box problem with -clear- command


From   "Steichen, Thomas" <STEICHT@rjrt.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Dialog box problem with -clear- command
Date   Wed, 26 Mar 2003 12:18:53 -0500

I have received a follow-up from StataCorp (James Hassell, in
particular) who has kindly clarified the issue with the -clear-
command and dialog boxes.  He writes (in part):
 
> Regarding the -clear- command; As noted -clear- invokes 
> -discard- which causes the dialogs to be closed and their 
> contents cleared.
> 
> The following is an excerpt from -help discard-.
> 
> "clears all class definitions and instances (see help classutil); 
> and closes all dialogs and clears their remembered contents 
> (see help dialogs)."
> 
> The reason -preserve- can't save the contents of dialogs, is 
> because, -preserve- only saves the data and not the contents
> of the class system. Therefore, if -clear- is invoked after
> a -preserve-, all class instances are cleared and not recoverable.

This makes it clear that that -clear- is not a command you want
to use in conjunction with a program that uses a dialog box.

Clearly, the right programming approach is to use the most minimal
"clearing" command that accomplishes the needs of a particular
program.  James wrote elsewhere:

> The -clear- command not only clears the dataset from memory,
> it also clears many other things too.
> 
>     Clear is equivalent to typing:
> 
> 	. version 8
> 	. drop _all
> 	. label drop _all        (see help label)
> 	. scalar drop _all       (see help scalar)
> 	. matrix drop _all       (see help matrix)
> 	. cluster drop _all      (see help cluster)
> 	. eq drop _all
> 	. constraint drop _all   (see help constraint)
> 	. postutil clear         (see help postutil)
> 	. _return drop _all      (see help _return)
> 	. discard                (see help discard)

In the particular instance I encountered, a third-party program
that I called within my own program (for which I was writing
the dialog box), used -clear- to allow -tabi- to automatically
retain its dataset as the current dataset.  Using -drop _all-
instead would have accomplished this same task without wiping out 
the whole active environment.  Alternatively, the -replace- option 
of -tabi- would have done the same thing.

Looking at the list of what -clear- does, it seems clear to
me that one should not programmatically use that command unless
no other approach suffices, especially if one intends for the 
environment to be restored with a subsequent -restore- command.

My thanks to James Hassell, StataCorp, for making this clear.

Tom Steichen


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