MATLAB Programming

Designing User Classes in MATLAB
Indexed Reference Using subsref and subsasgn
UserclassesimplementnewdatatypesinMATLAB.Itisusefultobeableto
access object data via an indexed reference, as is possible with the MATLAB
built-in data types. For example, if A is an array of class double, A(i) returns
the i th element of A.
As the class designer, you can decide what an index reference to an object
means. For example, suppose you define a class that creates polynomial
objects and these objects contain the coefficients of the polynomial.
An indexed reference to a polynomial object,
p(3)
could return the value of the coefficient of x 3 , the value of the polynomial at x
= 3, or something different depending on the intended design.
You define the behavior of indexing for a particular class by creating two class
methods - subsref and subsasgn. MATLAB calls these methods whenever a
subscripted reference or assignment is made on an object from the class. If
you do not define these methods for a class, indexing is undefined for objects
of this class.
In general, the rules for indexing objects are the same as the rules for indexing
structure arrays. For details, see “Structures” on page 2-75.
Behavior Within Class Methods
If A is an array of one of the fundamental MATLAB data types, then
referencing a value of A using an indexed reference calls the built-in MATLAB
subsref method. It does not call any subsref method that you might have
overloaded for that data type.
For example, if A is an array of type double, and there is an @double/subsref
method on your MATLAB path, the statement B = A(I) does not call this
method, but calls the MATLAB built-in subsref method instead.
The same is true for user-defined classes. Whenever a class method requires
the functionality of the overloaded subsref or subsassign, it must call the
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