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Properties Containing Objects

Assigning Objects as Default Property Values

MATLAB® evaluates property default values only once when loading the class. MATLAB does not reevaluate the assignment each time you create an object of that class. If you assign an object as a default property value in the class definition, MATLAB calls the constructor for that object only once when loading the class.

    Note:   Evaluation of property default values occurs only when the value is first needed, and only once when MATLAB first initializes the class. MATLAB does not reevaluate the expression each time you create an instance of the class.

For more information on the evaluation of expressions that you assign as property default values, see When MATLAB Evaluates Expressions.

Assigning to Read-Only Properties Containing Objects

When a class defines a property with private or protected SetAccess, and that property contains an object which itself has properties, assignment behavior depends on whether the property contains a handle or a value object:

  • Handle object – you can set properties on handle objects contained in read-only properties

  • Value object – you cannot set properties on value object contained in read-only properties.

Assignment Behavior

These classes illustrate the assignment behavior:

  • ReadOnlyProps – class with two read-only properties. The class constructor assigns a handle object of type HanClass to the PropHandle property and a value object of type ValClass to the PropValue property.

  • HanClass – handle class with public property

  • ValClass – value class with public property

classdef ReadOnlyProps
   properties(SetAccess = private)
      PropHandle
      PropValue
      
   end
   methods
      function obj = ReadOnlyProps
         obj.PropHandle = HanClass;
         obj.PropValue = ValClass;
      end
   end
end

classdef HanClass < handle
   properties
      Hprop
   end
end 

classdef ValClass
   properties
      Vprop
   end
end

Create an instance of the ReadOnlyProps class:

a = ReadOnlyProps
a = 

 ReadOnlyProps with properties:

    PropHandle: [1x1 HanClass]
     PropValue: [1x1 ValClass]

Use the private PropHandle property to set the property of the HanClass object it contains:

class(a.PropHandle.Hprop)
ans =

double
a.PropHandle.Hprop = 7;

Attempting to make an assignment to the value class object property is not allowed:

a.PropValue.Vprop = 11;

You cannot set the read-only property 'PropValue' of ReadOnlyProps.

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