Dependent property for subclasses

Why does the following inheritance not work?

class A < handle 

properties (Dependent) 
  a 
end 

methods 
  function this = A(a) 
    this.a = a; 
  end 

  function a = get.a(this) 
    a = this.a; 
  end 
end 

class B < A 

methods 
  function this = B(a) 
    this.a = a; 
  end 

  function a = get.a(this) 
    a = this.a+1; 
  end 
end 

The error is:

The method get.a does not refer to a valid property name

Answer 1

[Sai Veeramachaneni]

Hi,

get.a is not a valid function name, Valid function names begin with an alphabetic character, and can contain letters, numbers, or underscore only

Try changing it to getA instead of get.a

Hope it helps.

[Steven Lord]

The first paragraph of your answer is true, but that syntax is valid in MATLAB. It is used to define a property accessor method for the a property. See this documentation page for more information.

Answer 2

[Steven Lord]

You are only allowed to define a property accessor method for a property if

• the class in which the method is defined also defines the property
• the class does not include a properties block that defines that property but does allow dynamic properties (see the Set and Get Methods for Dynamic Properties documentation page linked in the See Also section), or
• the property is Abstract in its defining class, in which case a concrete subclass can define a property accessor method

See the "Restriction on Access Methods" section on this documentation page for more information.

No, a superclass defining a property in its properties block does not allow its subclasses to define a property accessor method. Doing so could allow the subclass to accept a value that would make the subclass instance not a valid superclass instance.

Consider a hierarchy where EquilateralTriangle inherits from Triangle. Triangle defines a property numSides and validates that this property always has value 3. [Yes, it should be a Constant property and not have a property accessor method, but this is a simplified example to illustrate a point.] If EquilateralTriangle could define a property accessor method that allows numSides to be 4 (due to a bug in the method) and you created an EquilateralTriangle with numSides equal to 4, it would not be a valid Triangle.

[Captain Karnage]

One issue I'm having is if you use an Abstract property - you can't use validation functions in the property block. That gives the error:

Using size and validation functions on an inherited property is not supported.

What I want to do, is I'm creating a class with two integer values. I'm trying to make subclasses where the precision of the two values is different in each subclass - but they all share the same methods in the superclass so I only have to write the methods once (more importantly - only have to EDIT the methods once when I have to make changes). The idea is I have a superclass, let's call it DInteger.. and I want subclasses DInt, DInt8, DInt16, DInt32, and Dint64. The two properties are I1 and I2 (and also a logical named sign).

If I could do what I wanted, the superclass, DInteger would validate using {mustBeInteger} which will allow any integer type or a floating type that is equal to an integer - then DInt would set the type of I1 and I2 as double, DInt8 would set them to uint8, up to Dint64 which would set them to uint64. I can use whatever validators in the superclass, but can't add any validators in the subclass. I can use validation in my constructors and other functions that set the properties, but that doesn't guarantee the property doesn't get set to a wrong type somewhere. Is there anyway to do that?