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How to remove user-defined objects from memory?

Asked by Chaitanya Jha on 7 Nov 2019
Latest activity Commented on by Chaitanya Jha on 8 Nov 2019
Hi, let's say I have two classes A_Class() and B_Class(). The A_Class() is defined something like this:
classdef A_Class < handle
properties
B;
end
methods
function obj = A_Class()
obj.B{1} = B_Class();
obj.B{2} = B_Class();
obj.B{3} = B_Class();
end
end
end
I create an object of class A_Class(),
A = A_Class;
Then I run the following command:
length(A.B)
and the answer is 3, which is correct. However, when I delete the object A.B{3} using the command delete(A.B{3}) the object gets deleted but when I check for length of B using command length(A.B) the answer is still 3, why? When I try to access A.B{3} matlab tells me that it is an invalid or deleted object, but still gives an answer 3 for the length of A.B why? How can make the answer 2, which is the correct answer. This is frustrating, I tried clearing the handle A.B{3} but that does not help. Any help will be appriciated, thanks a lot in advance :)

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1 Answer

Answer by Guillaume
on 7 Nov 2019
Edited by Guillaume
on 7 Nov 2019
 Accepted Answer

Note that this has nothing to do with objects. You don't seem to be understanding cell arrays.
Your B is a cell array. A cell array is simply a container. When you ask matlab length(B) you ask the length of the container. You've created a container with 3 slots, therefore its length is 3. It doesn't matter what is in the slot, an object, a lump of coal, or nothing, the length of the container is unchanged. Note that {} affects the content of a slot, not a slot itself. You use () to interact with the container itself.
B = {[1 2 3], 'a lump of coal', B_class}; %a container of length 3, containing various things.
B{3} = []; %replace the content of slot 3 with nothing. The container has still length 3
B(3) = []; %delete slot 3 from the container, regardless of what's in it. length is now 2

  2 Comments

A = A_Class;
length(A.B)
ans = 3
A.B(3) = [];
length(A.B)
ans = 2
Perfect! Thank you so much. Can't believe I was thinking that was because of how class-object relationship in Matlab.

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