MATLAB Answers

Unable to clear classes

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Jim Hokanson
Jim Hokanson on 23 Oct 2012
Answered: Fuad Numan on 4 Feb 2016
At times I am unable to clear classes in Matlab without restarting the program. This seems to be related to errors being thrown in the class. In other words, following an error I might make a change to the class and then call "clear classes" to reset everything. Also, since 95% of the time I am working with handle classes, this may be handle class related.
Some issues I have run across that I know are not currently the problem are: 1) storage of the class in a figure which is still open 2) the default value of a property being a class
Thanks, Jim
  12 Comments
Jim Hokanson
Jim Hokanson on 27 Nov 2012
I have confirmed with TMW that the example I provided below is a bug. Unfortunately I have not yet received a bug ID. One of the problems I identified (there may be more) is when children hold onto a reference of the parent object, and the parent holds onto a reference of the children. This only occurs when there are more than 2 children.
A workaround:
N = 4 %number of children
for iChild = 1:N
tempChildren(iChild) = child_class(parent_class);
end
parent_class.children = tempChildren;
%NOTE: In the child we have something like
function obj = child_class(parent_obj)
obj.parent = parent_obj;
The bug would occur in this case below: These are both handles clases
parent_class.children = child_class(parent_class,4)
function obj = child_class(parent_obj,N)
if nargin == 0
return
end
obj(N) = child_class;
for iObj = 1:N
obj(iObj) = child_class;
obj.parent = parent_obj;
end

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Accepted Answer

Jim Hokanson
Jim Hokanson on 27 Apr 2013
This is a bug:
It has been fixed in 2013a

More Answers (7)

Sean de Wolski
Sean de Wolski on 24 Oct 2012
Hi Jim,
Are you saving the objects to or loading from a *.mat file? If so please see:
This bug report doesn't highlight the workaround though, which is to not store the *.mat files with -v7.3 formatting.
  7 Comments
Matt J
Matt J on 7 Nov 2012
Never mind, I was able to reproduce the problem with
class_1(10);
clear classes;
This was even without the directory structure you specified, and it was in R2012a. Also, "clear classes" always gives me a warning.

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Malcolm Lidierth
Malcolm Lidierth on 7 Nov 2012
Object references can leak via userdata or appdata, callbacks, the variable editor etc. Try closing all figures - but probably close the variable editor first.
With handle classes I have taken to maintaing a list in the figure appdata area maintained by calling a common superclass method from the constructors, and adding a DeleteFcn callback that calls a static superclass method to delete any remaining valid handle objects when a figure closes. A bit of a pain but it seems to work.

Matt J
Matt J on 24 Oct 2012
Just a thought. Try doing REHASH. Then clear classes again.
  2 Comments
Matt J
Matt J on 24 Oct 2012
what about my latest comments/questions above?

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Daniel Shub
Daniel Shub on 25 Oct 2012
Two related, but not duplicate, questions are
There was also a related question sometime in the past few months where it eventually seemed like the problem was a bug (the problem disappeared in some release) It involved two classes calling each other. I can no longer find the question (which isn't surprising give the search capabilities of Answers).

Matt J
Matt J on 7 Nov 2012
Edited: Matt J on 8 Nov 2012
Based on your example with class_1 and class_2, I think the problem is related to the fact that you are creating handle objects which contain shared copies of themselves (the temp property is passed copies of obj itself in the constructor). I can't explain why the problem occurs only for N>2, however, it's easy to see that you create a chicken-and-egg situation when MATLAB tries to delete an object of class_1: before MATLAB can delete an object of class_1, it must first delete all the data in the properties that it contains. However, the properties of the class_1 object contain the object itself!
Is there any way you can settle for unshared copies of class_1 in temp?
  5 Comments
Malcolm Lidierth
Malcolm Lidierth on 9 Nov 2012
Does subclassing hgsetget instead of handle help? Standard handle graphics always have a parent/child hierarchy.
Do the classes need to be in the same package?
I do not recall recognizing this behaviour in my own classes (but all use hgsetget and never use packages - in MATLAB anyway).
However, I do have isvalid tests in the delete methods on the instance being deleted because function delete(obj) sometimes gets a valid and sometimes an invalid obj. I think this problem may (??) be related - at what stage during deletion does isvalid return false when there are leaks, and what order does MATLAB delete a circular reference. obj.delete() can get called even when obj.isvalid() returns false. Is it the MATLAB delete equivalent of referencing "this" in a constructor in e.g. Java.

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Chris Wiak
Chris Wiak on 4 Feb 2016
I have the same problem in Matlab 2015b. 'clear classes' throws a warning. Any thoughts on this one?

Fuad Numan
Fuad Numan on 4 Feb 2016
ClassStore.Class1=struct();
This will clear a specific variable (Class1) from the main Class (ClassStore).

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