Programming

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

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