Establishing an object precedence enables MATLAB® to determine which of possibly many versions of an operator or function to call in a given situation.
For example, consider the expression
objectA + objectB
Ordinarily, objects have equal precedence and the method associated with the leftmost object is called. However, there are two exceptions:
User-defined classes have precedence over MATLAB fundamental classes (numeric, logical,
char, cell,
struct, and function handle) and certain built-in
classes.
User-defined classes can specify their relative precedence
with respect to other user-defined classes using the InferiorClasses attribute.
In Class Design for Polynomials, the polynom class
defines a plus method that enables the addition
of DocPolynom objects. Given the object p:
p = DocPolynom([1 0 -2 -5])
p =
x^3-2*x-5
the expression:
1 + p
ans =
x^3-2*x-4
calls the DocPolynom plus method
(which converts the double, 1, to a DocPolynom object
and then implements the addition of two polynomials). The user-defined DocPolynom class
has precedence over the built-in double class.
You can specify the relative precedence of user-defined classes
by listing inferior classes in a class attribute. The InferiorClasses property
places a class below other classes in the precedence hierarchy. Define
the InferiorClasses property in the classdef statement:
classdef (InferiorClasses = {?class1,?class2}) myClass
This attribute establishes a relative priority of the class being defined with the order of the classes listed.
If objectA is above objectB in
the precedence hierarchy, then the expression
objectA + objectB
calls @classA/plus.m.
Conversely, if objectB is above objectA in
the precedence hierarchy, then the MATLAB runtime calls @classB/plus.m.