Non-scalar enumerations of class double

Why am I not able to create an enumeration of double arrays? Consider the following simple case.

    classdef Quaternion < double    
        enumeration
            U([ 1, 0; 0,  1])
            I([1i, 0; 0,-1i])
            J([ 0,-1; 1,  0])
            K([ 0,1i;1i,  0])
        end    
    end

To me, everything seems in order. The enumerated values are distinct, and of the appropriate class. But when I call the constructor I get the following error.

    >> u = Quaternion.
    In class 'Quaternion', enumeration member named 'U' must be scalar.

I scoured the documentation, and couldn't find anything that explicitly stated this was not possible.

If this is simply not possible, perhaps Mathworks should consider making this a new feature. Seems like a no-brainer to me.

Answer 1

[Captain Karnage]

There's a few problems with attempting to do this in MATLAB. First, though you can make an enumeration a subclass of a built-in type - you can't do it unless your enumerations are each a specific scalar value of the superclass type. Instead, you should make it not a subclass of a built in type and instead make properties of that type, as follows:

classdef Quaternion
    
    enumeration
        U( [ 1,  0; 0,   1] )
        I( [ 1i, 0; 0, -1i] )
        J( [ 0, -1; 1,   0] )
        K( [ 0, 1i; 1i,  0] )
    end
    
    properties
        q    double;
    end
    
    methods

        function obj = Quaternion(q)
            arguments
                q    (2, 2)    double;
            end
            obj.q = q;
        end
    
    end

end

You could also make the constructor have 2 or 4 inputs, each representing either a row or individual element of your matrix, if you wanted - and could map that to a single or multiple properties as well. For example, the constructor could be obj = Quaternion(a,b,c,d) and then set obj.q = [ a, b; c, d] and validate that each input is a 1x1 scalar if you want to do validation.