MATLAB Object-Oriented Programming

Objects Passed to Functions

MATLAB passes all variables by value. When you pass an object to a function, MATLAB

copies the value from the caller into the parameter variable in the called function.

However, MATLAB supports two kinds of classes that behave differently when copied:

• Handle classes — a handle class instance variable refers to an object. A copy of a
  handle class instance variable refers to the same object as the original variable. If a
  function modifies a handle object passed as an input argument, the modification
  affects the object referenced by both the original and copied handles.


• Value classes — the property data in an instance of a value class are independent of
  the property data in copies of that instance (although, a value class property could
  contain a handle). A function can modify a value object that is passed as an input
  argument, but this modification does not affect the original object.

See “Comparison of Handle and Value Classes” on page 7-2 for more information on the

behavior and use of both kinds of classes.

Passing Value Objects

When you pass a value object to a function, the function creates a local copy of the

argument variable. The function can modify only the copy. If you want to modify the

original object, return the modified object and assign it to the original variable name. For

example, consider the value class, SimpleClass :

classdef SimpleClass

properties

Color

end

methods

function obj = SimpleClass(c)

if nargin > 0

obj.Color = c;

end

end

end

end

Create an instance of SimpleClass, assigning a value of red to its Color property:

obj = SimpleClass('red');

Pass the object to the function g, which assigns blue to the Color property:

5 Class Definition—Syntax Reference