Programming and Data Types

Object Precedence

Object precedence is a means to resolve the question of which of possibly many versions of an operator or function to call in a given situation. Object precedence enables you to control the behavior of expressions containing different classes of objects. For example, consider the expression

objectA + objectB

Ordinarily, MATLAB assumes that the objects have equal precedence and calls the method associated with the leftmost object. However, there are two exceptions:

• User-defined classes have precedence over MATLAB built-in classes.
• User-defined classes can specify their relative precedence with respect to other user-defined classes using the inferiorto and superiorto functions.

For example, in the section Example - A Polynomial Class the polynom class defines a plus method that enables addition of polynom objects. Given the polynom object p

p = polynom([1 0 -2 -5])

p =

    x^3-2*x-5

The expression,

1 + p

ans =

    x^3-2*x-4

calls the polynom plus method (which converts the double, 1, to a polynom object, and then adds it to p). The user-defined polynom class has precedence over the MATLAB double class.

The Portfolio subsref Method

Specifying Precedence of User-Defined Classes