Improve Version Compatibility with Default Values

Version Compatibility

Default property values can help you implement version compatibility for saved objects. For example, suppose that you add a property to version 2 of your class. Having a default value enables MATLAB^® to assign a value to the new property when loading a version 1 object.

Similarly, suppose version 2 of your class removes a property. If a version 2 object is saved and loaded into version 1, your loadobj method can use the default value from version 1.

Using a Default Property Value

The EmployeeInfo class shows how to use property default values as a way to enhance compatibility among versions. Version 1 of the EmployeeInfo class defines three properties — Name, JobTitle, and Department.

classdef EmployeeInfo
   properties
      Name
      JobTitle
      Department
   end
end

Version 2 of the EmployeeInfo class adds a property, Country, for the country name of the employee location. The Country property has a default value of 'USA'.

classdef EmployeeInfo
   properties
      Name
      JobTitle
      Department
      Country = 'USA'
   end
end

The character array, 'USA', is a good default value because:

MATLAB assigns an empty double [] to properties that do not have default values defined by the class. Empty double is not a valid value for the Country property.
In version 1, all employees were in the USA. Therefore, any version 1 object loaded into version 2 receives a valid value for the Country property.

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