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From: graver@gull.cis.ufl.edu (Justin Graver)
Newsgroups: comp.lang.smalltalk
Subject: Re: Mysterious appearances of Doits  in V286
Message-ID: <25546@uflorida.cis.ufl.EDU>
Date: 21 Nov 90 21:11:51 GMT
References: <2562@runxtsa.runx.oz.au>
Sender: news@uflorida.cis.ufl.EDU
Organization: UF CIS Dept.
Lines: 51

In article <2562@runxtsa.runx.oz.au> timm@runxtsa.runx.oz.au (Tim Menzies) writes:
>Does anyone else get  mysterious "Doit" methods appearing in their
>Smalltalk/V 286 image? 
>
>The manual says that only Undefined object has a "Doit" method
>(though lord knows what it  does). But my virgin Smalltak V 286
>images  tells  me (via Smalltalk implementersOf:  #Doit) that  there
>are Doits in  Array, Interval, etc, etc. Sometimes,  in the classes
>that I've created, Doits  appear. I  delete them and nothing
>untoward happens.  


I can't speak for Smalltalk V 286, but for Smalltalk-80 here is the
story.  Whenever you select an expression and "doit" from a text menu
the following scenario occurs:

	1.  the text controller grabs the text and sends it to the
		compiler to be evaluated

	2.  to evaluate the text string, the compiler creates a
		"fake" method with the selector #Doit whose
		body is the selected text.

	3.  this method is then compiled and installed in some
		appropriate class (usually determined by the
		context of the text window, e.g. a broswer)
		just as if it had been "accepted" in a broser

	4.  the compiler next creates a new instance of the
		appropriate class and sends it the #Doit message,
		saving the result, which will be eventually returned
		to the user.

	5.  if all goes well, the fake method is removed and the
		result object is returned as the result of the "doit"

	6.  however, if something goes wrong during the execution
		of the method, or a debugger is closed without
		finishing the evaluation, the fake method never
		gets removed from the class (hence the possibility
		of various rogue implementations of the #Doit method
		in classes throughout the image).

Hope this helps.

	Justin Graver
	University of Florida
	E301 CSE
	Gainesville, FL  32611
	(904) 392-1507
	graver@cis.ufl.edu