class1 as property of class2, class1 property initialization?

I have a class:

classdef class1
    properties
        prop1 = 1;
    end
end 

and I can easily access prop1 with:

test = class1
test.prop1
ans = 1

If I then put class1 as a property into another class e.g.:

classdef mainClass
    properties
        class1
    end
end

I would like to access class1 propr 1 through mainClass. So I try the following but get an error:

>> test.class1(1).prop1
Index exceeds the number of array elements. Index must not exceed 0.

Why is prop1 not initialized to the value 1? Thanks

Answer 1

[Benjamin Kraus]

In your definition of mainClass you created a property with the name class1, not the type class1.

This is what you want:

classdef mainClass
    properties
        class1 (1,1) class1
    end
end

Just be careful using this approach. If class1 is a handle class, then all instances of mainClass will share the same class. In that case, you are better off with this approach:

classdef mainClass
    properties
        class1
    end
    methods
        function obj = mainClass()
            obj.class1 = class1;
        end
    end
end

You may also want to reconsider having a property name that matches a class name. It works, but it may be confusing.

[SoderlingPotro]

Thank you Benjamin. I agree about the class name being the same as the type being confusing. I understand the class1 attribute saying that this property must be of type class1, however I thought the (1,1) was just property validation when assigning values to the property (object). Why does it also initialize the object? Is it because it would violate the validation if it initialized as empty?

[Benjamin Kraus]

You are correct. The default value can't be an empty vector because of the size validation, so by specifying that the size must be a scalar object of class class1, MATLAB will automatically (attempt to) create a scalar instance of that object as the default value of the property. Unless you also specify a default value, the object will be created by calling the class constructor with no input arguments. Without the (1,1) MATLAB will use a default value of class1.empty().