Define Property Attributes

Property attributes, which add details to a property, provide a layer of control to your properties. In addition to the MATLAB^® property attributes and property validation, System objects can use Nontunable or DiscreteState. To specify multiple attributes, separate them with commas.

Specify Property as Nontunable

By default all properties are tunable, meaning the value of the property can change at any time.

Use the Nontunable attribute for a property when the algorithm depends on the value being constant once data processing starts. Defining a property as nontunable may improve the efficiency of your algorithm by removing the need to check for or react to values that change. For code generation, defining a property as nontunable allows the memory associated with that property to be optimized. You should define all properties that affect the number of input or output ports as nontunable.

When you use the System object™, you can only change nontunable properties before calling the object or after calling the release function. For example, you define the InitialValue property as nontunable and set its value to 0.

properties (Nontunable)
   InitialValue = 0;
end

Specify Property as DiscreteState

If your algorithm uses properties that hold state, you can assign those properties the DiscreteState attribute. Properties with this attribute display their state values via the getDiscreteStateImpl when users call getDiscreteState. The following restrictions apply to a property with the DiscreteState attribute,

Numeric, logical, or fi value, but not a scaled double fi value
Does not have any of these attributes: Nontunable, Dependent, Abstract, Constant.
No default value
Not publicly settable
GetAccess = Public by default
If you define the property as discrete state, you do not need to manually save or overwrite the object using saveObjectImpl or loadObjectImpl.

For example, you define the Count property as a discrete state:

properties (DiscreteState)
   Count;
end

Insert Custom Property

Use the Custom Property dialog box to define a new property with selected attributes. To add custom property, select the Insert Property drop-down from the Editor toolstrip and select Custom Property.... Use the dialog box to set the property access, System object attributes, and MATLAB property attributes for your custom properties.

Access

Access	Setting	Description
`SetAccess` and `GetAccess`	`public`	Property can be accessed by any other code in the same System object or another System object that references it.
	`protected`	Property can be used only by code in the same System object or in a subclass.
	`private`	Property can be accessed only by code in the same System object.
	`immutable`	You can set this property value only when you create the System object. You cannot change the property value. This setting applies only to `SetAccess`.

System Object Attributes

Attribute	Description
Logical	Limits the property values to logical scalar values. Any scalar value that can be converted to a logical is also valid, such as 0 or 1.
Nontunable	Prevents changes to the property values while system is running.
DiscreteState	Holds state value.
PositiveInteger	Limits the property value to a positive integer value.

MATLAB Property Attributes

Attribute	Description
Constant	This property has only one value in all instances of the class.
Hidden	The property is not shown in a property list.
Dependent	The property value is not stored in the object. The `set` and `get` functions cannot access the property by indexing into the object using the property name.

To create the property with the selected attributes, click Insert. MATLAB Editor inserts the property into your code.

Example Class with Various Property Attributes

This example shows two nontunable properties, a discrete state property, and also MATLAB class property validation to set property attributes.

classdef Counter < matlab.System
% Counter Increment a counter to a maximum value

  % These properties are nontunable. They cannot be changed 
  % after the setup method has been called or while the
  % object is running.
  properties (Nontunable)
      % The initial value of the counter
      InitialValue = 0
      % The maximum value of the counter, must be a positive integer scalar
      MaxValue (1, 1) {mustBePositive, mustBeInteger} = 3
  end
  
  properties
      % Whether to increment the counter, must be a logical scalar
      Increment (1, 1) logical = true
  end
   
  properties (DiscreteState)
      % Count state variable
      Count
  end
      
  methods (Access = protected)
      % Increment the counter and return its value
      % as an output
  
      function c = stepImpl(obj)
          if obj.Increment && (obj.Count < obj.MaxValue)
              obj.Count = obj.Count + 1;
          else
              disp(['Max count, ' num2str(obj.MaxValue) ' ,reached'])
          end
          c = obj.Count;
      end
      
      % Setup the Count state variable
      function setupImpl(obj)
          obj.Count = 0;
      end
      
      % Reset the counter to one.
      function resetImpl(obj)
          obj.Count = obj.InitialValue;
      end
  end
end