MATLAB: Retrieving/storing the state of a handle

handleoop

Hi,

Is it possible to retrieve the old state of a modified handle object? more concretely, suppose a have a class such as

classdef myclass < handle
...
end

and I create an instance of myclass, e.g. h0=myclass(varargin) and create a copy h=h0; I understand that if I modify h0, then h will also be modified. My problem is that I would like to pass h0 through a function that modifies it randomly and I need to repeat the exercise several times and see how the results differ. In order to be able to do that, I need the original state h.

Is there anyway to achieve this?

Thanks,

Best Answer

You could make your class a value class rather than a handle class or you could make your class Copyable. By subclassing matlab.mixin.Copyable the class inherits a copy method that:

Copies data without calling class constructors or property set functions and therefore produces no side effects.
Enables subclasses to customize the copy behavior

When you need to make random changes to the object that won't affect the "main" instance of your object, pass a copy. When you want to have two instances that have normal handle semantics (changing one changes the other) use non-indexed assignment to create the second instance.

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MATLAB: Lisning for a subclass property

First, a matter of terminology. Your subclass is not a subclass at all. A subclass derives from the main class. In matlab OOP this implies the following definition:

classdef subclass < mainclass

Your subclass is just a standard class that happens to be a member of your main class. It would be very odd for a main class to instantiate a subclass (except through factory methods), anyway.

In any case, If you want to listen to the property changes of your member class, it is these properties you need to set observable and these properties you need to attach a listener. At present, the only thing you'll detect is if your subclass member is changed to a new instance. That is you'll detect this:

m.subclass = class_subclass; %assign a new class_subclass to the member property of m

MATLAB: How to copy an object that is not a graphic one

In general, you would have to write a copy() method specific to the needs of your class. The copy() method would have to call the class constructor with suitable arguments to generate a copy.

If your class is sufficiently simple that a copy can be made just by dot-indexing all of the non-Dependent, public property values and writing them to a second object,

   objcopy.prop1 = obj.prop1;
   objcopy.prop2 = obj.prop2;
   etc...

then you can just use my attached copyprops() utility, which automates this.

Best Answer

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MATLAB: Lisning for a subclass property

MATLAB: How to copy an object that is not a graphic one

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