dataBank: zef_dataBank_setData causes a memory leak and print issues of some functions

[JoonasJL]

Function zef_dataBank_setData has the following if-chain leading it to call itself infinitely, or a bit less

if zef.dataBank.loadParents
    
        zef.dataBank.hash=reverse(zef.dataBank.hash);
        zef.dataBank.hash=extractAfter(zef.dataBank.hash, '_');
        zef.dataBank.hash=reverse(zef.dataBank.hash);

        if ~strcmp(zef.dataBank.hash, 'node') 
            **zef_dataBank_setData;**
        end   

Now that the zef structure is taken in the function, this will cause out of memory error.

It seems also that some of the functions are missing a semicolon in the starting lines

if nargin == 0
zef = evalin('base','zef')
end

Personally, I could make some edits to make this work more efficiently because I have done a lot of work with fields and became good at it, but on the other hand my time is currently limited and the style of scripting is so far from mine that it will take a while for me to understand what there is happening under the hood.

[SeSodesa]

If zef was written as a handle class instead of being a struct, the copy-on-write semantics of value classes like structs would not be applied to it. Since structs are value classes, when one does

zef2 = zef;

zef2.field = value;

the value behind zef2 gets copied in memory, so that zef and zef2 no longer point at the same instance. If zef was a handle class, this would not happen, and both zef and zef2 would keep pointing to the same value on the heap or dynamic memory, which is where Matlab stores everything except variable symbols or names, much like Python does.

Why is this important? Because when you pass a name such as zef into a function in Matlab, Matlab essentially treats it like zef2 was treated above, as a reference to an existing value but with a differently scoped name. Whether the value gets copied when/if the function assigns something to a field of the input depends entirely on whether the input argument is a value or a handle class.

Here is a comparison between value- and handle classes: https://se.mathworks.com/help/matlab/matlab_oop/comparing-handle-and-value-classes.html.

[SeSodesa]

There were some tricks around avoiding the unnecessary copying of value- or copy-on-write classes, but these are not always very reliable, since functions have to be written in a very specific way for it to work: https://se.mathworks.com/help/matlab/matlab_prog/avoid-unnecessary-copies-of-data.html.

[SeSodesa]

Handle classes can be copied, if instead of inheriting from the handle class directly, you inherit from its subclass, matlab.mixin.Copyable:

>> superclasses("matlab.mixin.Copyable")

Superclasses for class matlab.mixin.Copyable:

    handle

Once you do MyHandleClass < matlab.mixin.Copyable, you can rewrite the copy and copyElement methods provided by the superclass to customize the copying behaviour: https://se.mathworks.com/help/matlab/matlab_oop/custom-copy-behavior.html. You then call these methods explicitly, when you want a copy of the value behind variable pointing to a class instance.