MATLAB Object-Oriented Programming

Role of size Function in Custom Displays

In this section...

“How size Is Used” on page 18-10

“Precautions When Overloading size” on page 18-10

How size Is Used

In the process of building the custom display, CustomDisplay methods call the size

function at several points:

• disp calls size to determine which state handler method to invoke.


• The default getHeader method calls size to determine whether to display a scalar or
  nonscalar header.


• The default displayPropertyGroups method calls size to determine if it should
  look up property values when the property group is a cell array of property names. By
  default, only scalar objects display the values of properties.

Precautions When Overloading size

If your class overloads the size function, then MATLAB calls the overloading version. You

must ensure that the implementation of size is consistent with the way you want to

display objects of the class.

An unusual or improper implementation of size can result in undesirable display

behavior. For example, suppose a class overloads size reports an object as scalar when it

is not. In this class, a property list consisting of a cell array of strings results in the

property values of the first object of the array being displayed. This behavior can give the

impression that all objects in the array have the same property values.

However, reporting an object as scalar when in fact the object is empty results in the

object displaying as an empty object array. The default methods of the CustomDisplay

interface always determine if the input is an empty array before attempting to access

property values.

As you override CustomDisplay methods to implement your custom object display,

consider how an overloading size method can affect the result.

18 Customizing Object Display