MATLAB: Predefined “Settings” in R2011b

class

Dear Forum,

in R2010b I used a larger struct named "Settings", used to collect several settings. I saved this struct to a mat-file and tried to reload it later on. When accessing the (loaded) Settings, Matlab R2011b gives:

ans=
Settings handle with no properties.
  Methods, Events, Superclasses

It seems, that in R2011b a new class named Settings came onto the field.

My question:

Is this problematic? How to override? Should I override? What would be the best choice to do?

Thanks for any answer,

Alexander

Best Answer

Where and how are you trying to reload them?

In 11b I get the following:

>> which Settings -all
Settings is a built-in method  % Settings constructor
>> Settings = pi
Settings =
      3.1416
>> which Settings -all
Settings is a variable.
Settings is a built-in method  % Shadowed Settings constructor

So you're right that there is a name conflict, but a local variable should (as always) take precedence. So I'm wondering if this is a problem with zapping variables into existence inside a function.

If you have load foo in a function (and Settings is a variable in foo.mat) then you will run into name conflict problems. The solution is to use the functional form of load:

x = load('foo.mat');
Settings = x.Settings;
clear('x');

More info: http://www.mathworks.com/help/techdoc/import_export/braietb-1.html#bsdnp13

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MATLAB: How does MATLAB solve the diamond problem in multiple inheritance

The problem you are referring to is commonly known as "the diamond problem": 2 classes B and C inherit from A and a class D inherits from both B and C; if a method in D calls a method defined in A (and does not override it), and B and C have overridden the method differently, there is an ambiguity as to which class D inherits from (B or C?). C++ solves this issue using virtual inheritance. In MATLAB, this ambiguity could arise for properties, methods and events if these are defined with the same name by the respective superclasses (i.e., B and C). The steps to be taken in order to avoid such conflicts are discussed on the following page:

http://www.mathworks.com/help/releases/R2016a/matlab/matlab_oop/subclassing-multiple-classes.html

For methods, and as in C++, a conflict occurs only if the superclasses (B and C) inherit a method from a common base class (ancestor A) and override it. As mentioned on the page above, one way to resolve such a conflict is to have one superclass define the method as sealed (by setting the Sealed attribute to True), in which case the subclass adopts the sealed method definition (no ambiguity). The attached example illustrates the diamond problem in MATLAB with 4 classes A, B, C and D as described above.

If you try to create a D object as follows, it results in an error:

>> dobj = D

Error using D

Method 'Amethod' defined in class 'D' has 2 or more conflicting definitions.

To see how this could be resolved by defining the method as sealed in one of the superclasses, just uncomment the commented lines in B.m and run the following commands:

>> dobj = D;
A constructor called
B constructor called
A constructor called
C constructor called
D constructor called
>> dobj.Amethod
B version of Amethod called

Again, the diamond problem would not be there if D overrides Amethod, which could be thought of as the simplest way to resolve the conflict (though not always applicable).

In general, we recommend implementing only one unrestricted superclass and defining all methods in all other superclasses as abstract in order to save oneself the effort of resolving the potential conflicts involved when defining a subclass from multiple classes.

MATLAB: Setter method does not work on inherited class

You're using handle syntax to set the property of your class, yet your class is a value class. Either change your setFoo to:

function obj = setFoo(obj, foo)
   obj.foo = foo;
end

and call it with:

test = test.setFoo(10);

or derive from handle:

classdef Foo < matlab.mixin.Heterogeneous & handle

Also, you can create setter and getter for the class properties, using this syntax

function set.foo(obj, value) %for handle class
   obj.foo = value;
end
function obj = set.foo(obj, value) % for value class
   obj.foo = value;
end

which you call simply with:

obj.foo = 10; %for value and handle class.

Best Answer

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MATLAB: How does MATLAB solve the diamond problem in multiple inheritance

MATLAB: Setter method does not work on inherited class

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