Using 'optional' properties in a MATLAB class - matlab

Question

I've a question concerning classes in MATLAB.
I'm writing a parser, that doesn't always have the same input. Some variables are not defined at all times. Here is a short mock up script:
test_parser.m
classdef test_parser < matlab.mixin.Copyable
properties (AbortSet = true)
a
b
end
end
make_class.m
function result = make_class(array)
result = test_parser;
result.a = array(1);
if length(array)>1
result.b=array(2);
end
end
Now calling from the command window with different input lengths:
>> make_class([10])
ans =
test_parser with properties:
a: 10
b: []
>> make_class([10,20])
ans =
test_parser with properties:
a: 10
b: 20
In both cases the variable b is a property of test_parser, as specified. My wish would be, that b is optional, so just present if there is b in the input.
What is the best way to achieve this? I guess an optional parameter is not really a property?

Answer 1

If you want optional properties, you can inherit your class from dynamicprops. You can then add properties on the fly using the command addprop, test whether a property exists using isprop, and even respond to properties being added or removed by listening to the events PropertyAdded and PropertyRemoved.
In your example, you would then use:
classdef test_parser < matlab.mixin.Copyable & dynamicprops
properties (AbortSet = true)
a
end
end
function result = make_class(array)
result = test_parser;
result.a = array(1);
if length(array)>1
result.addprop('b')
result.b=array(2);
end
end
>> make_class([10])
ans =
test_parser with properties:
a: 10
>> make_class([10,20])
ans =
test_parser with properties:
a: 10
b: 20