MATLAB Programming

9 Classes and Objects
How MATLAB Determines Which Method to Call
This section covers
• “Selecting a Method” on page 9-72
• “Querying Which Method MATLAB Will Call” on page 9-75
In MATLAB, functions exist in directories in the computer’s file system. A
directory may contain many functions (M-files). Function names are unique
only within a single directory (e.g., more than one directory may contain a
function called pie3). When you type a function name on the command line,
MATLAB must search all the directories it is aware of to determine which
function to call. This list of directories is called the MATLAB path.
When looking for a function, MATLAB searches the directories in the order
they are listed in the path, and calls the first function whose name matches
thenameofthespecifiedfunction.
If you write an M-file called pie3.m and put it in a directory that is searched
before the specgraph directory that contains the MATLAB pie3 function,
then MATLAB uses your pie3 function instead.
Object-oriented programming allows you to have many methods (MATLAB
functions located in class directories) with the same name and enables
MATLAB to determine which method to use based on the type or class of the
variables passed to the function. For example, if p is a portfolio object, then
pie3(p)
calls @portfolio/pie3.m because the argument is a portfolio object.
Selecting a Method
When you call a method for which there are multiple versions with the same
name, MATLAB determines the method to call by:
• Looking at the classes of the objects in the argument list to determine
which argument has the highest object precedence; the class of this object
controlsthemethodselectionandiscalledthedispatch type.
9-72