Why Overload Operators
By implementing operators that are appropriate for your class, you can integrate objects of your class into the MATLAB® language. For example, objects that contain numeric data can define arithmetic operations like
- so that you can use these objects in arithmetic expressions. By implementing relational operators, you can use objects in conditional statements, like
How to Define Operators
You can implement MATLAB operators to work with objects of your class. To implement operators, define the associated class methods.
Each operator has an associated function (e.g., the + operator has an associated
plus.m function). You can implement any operator by creating a class method with the appropriate name. This method can perform whatever steps are appropriate for the operation being implemented.
For a list of operators and associated function names, see MATLAB Operators and Associated Functions.
Object Precedence in Operations
User-defined classes have a higher precedence than built-in classes. For example, suppose
q is an object of class
p is a user-defined class. Both of these expressions generate a call to the
plus method in the user-define class, if it exists:
q + p p + q
Whether this method can add objects of class
double and the user-defined class depends on how you implement the method.
q are objects of different classes, MATLAB applies the rules of precedence to determine which method to use.
For more information on how MATLAB determines which method to call, see Method Invocation.
Overloaded operators retain the original MATLAB precedence for the operator. For information on operator precedence, see Operator Precedence.
Sample Implementation — Addable Objects
Adder class implements addition for objects of this class by defining a
Adder defines addition of objects as the addition of the
NumericData property values. The
plus method constructs and returns an
Adder object whose
NumericData property value is the result of the addition.
Adder class also implements the less than operator (
<) by defining a
lt method. The
lt method returns a logical value after comparing the values in each object
classdef Adder properties NumericData end methods function obj = Adder(val) obj.NumericData = val; end function r = plus(obj1,obj2) a = double(obj1); b = double(obj2); r = Adder(a + b); end function d = double(obj) d = obj.NumericData; end function tf = lt(obj1,obj2) if obj1.NumericData < obj2.NumericData tf = true; else tf = false; end end end end
Using a double converter enables you to add numeric values to
Adder objects and to perform addition on objects of the class.
a = Adder(1:10)
a = Adder with properties: NumericData: [1 2 3 4 5 6 7 8 9 10]
Add two objects:
a + a
ans = Adder with properties: NumericData: [2 4 6 8 10 12 14 16 18 20]
Add an object with any value that can be cast to double:
b = uint8(255) + a
b = Adder with properties: NumericData: [256 257 258 259 260 261 262 263 264 265]
b using the
a < b
ans = 1
Ensure that your class provides any error checking required to implement your class design.
MATLAB Operators and Associated Functions
The following table lists the function names for MATLAB operators. Implementing operators to work with arrays (scalar expansion, vectorized arithmetic operations, and so on), can also require modifying indexing and concatenation. Use the links in this table to find specific information on each function.
Method to Define
Right element-wise division
Left element-wise division
Matrix right division
Matrix left division
Less than or equal to
Greater than or equal to
Not equal to
Complex conjugate transpose