Thanks for your comment Bill. I need to learn more about good exception
handling for my own applications.
What I was surprised about was that nil appeared to receive a #do: but
not raise an error, and that next step in execution was
OrderedCollection>>do: .
Anyway, saving the sketch, closing the image, and the next day opening
the sketch has cleared the error.
Ben
Schwab,Wilhelm K wrote:
Ben,
I can't comment on the workings of Dr. Geo, but since you ask about #do:, nil, least
surprise etc., I can tell you that errors are your friends. Note that there is a
difference between sending #do: to nil (would you really expect "nothing" to
know how to iterate its contents?) and sending #do: to a collection that contains
elements, some of which happen to be nil? In the latter case, would it really be
non-surprising to have nil elements treated differently from their peers? Would you have
them treated differently only if nil encounters a problem doing what is asked of it? In
that case, #do: would have to trap and suppress errors, at least for nil entries.
All of that sounds pretty surprising to me. Eventually, it will to you too.
Happy Smalltalking!
Bill
________________________________________
From: [email protected]
[[email protected]] On Behalf Of Ben Coman
[[email protected]]
Sent: Saturday, October 22, 2011 2:36 PM
To: [email protected]
Subject: [Pharo-project] [BUG]UndefinedObject(Object)>>doesNotUnderstand:
#update
I was using DrGeo for the first time from the bundled release 11.08 on
Windows 7. About 30 minutes in I drew three equally intersecting
circles, added a reflection line with each circle reflected. I added a
free point with a middle (I think to a circle) and was trying to add a
locus.
When moving any of the points defining the circles I am getting a dozen
or more cascading MNUs down the screen. Moving the reflection line
still works okay.
The error occurs in following method...
DrGeo>>updateDirtyCostumes
self presenter tool costumes do: [ :each | each update ].
self area changed
In the debugger inspecting "self presenter tool costumes" returns nil.
While I can't judge whether returning nil is valid here, as a Smalltalk
newbie what I am really interested in is:
1. The semantics of sending a "do:" message to nil. By the principle of
least surprise I would expect that it would do ...nothing, whereas here
it tries later sending the "update" method to it.
2. Why in lines 0027 and 0641 is the "do:" method received by
OrderedCollection and not UndefinedObject? Actually I can't see "do:" in
the hierarchy of UndefinedObject, so why does UndefinedObject not raise
a MNU for "do:" ?
The image with the error is available at...
http://blog.openinworld.com/miscfiles/DrGeo-updateDirtyCostumes-MNU-2011-10-22-btc.zip
The stack trace generated by the <Mail out bug report> menu item is
below. I wasn't sure how much of it to cut or leave, so I've left it all.
------------------8<-------------------------
00000001 22 October 2011 10:27:03 pm
00000002
00000003 VM: Win32 - IX86 - NT - Squeak3.10.2 of 11 February 2010
[latest update: #9314]
