Visual Basic 2005: A Developer's Notebook

Use Operators with Custom Objects

Every VB programmer is familiar with the arithmetic operators for addition (+), subtraction (-), division (/), and multiplication (*). Ordinarily, these operators are reserved for .NET numeric types, and have no meaning when used with other objects. However, in VB .NET 2.0 you can build objects that support all of these operators, as well as the operators used for logical operations and implicit conversion). This technique won't make sense for business objects, but it is extremely handy if you need to model mathematical structures such as vectors, matrixes, complex numbers, or—as demonstrated in the following example—fractions.

Note

Tired of using clumsy syntax like ObjA.Subtract(ObjB) to perform simple operations on your custom objects? With VB's support for operator overloading, you can manipulate your objects as easily as ordinary numbers.

How do I do that?

To overload an operator in Visual Basic 2005, you need to create a special operator method in your class (or structure). This method must be declared with the keywords Public Shared Operator, followed by the symbol for the operator (e.g., +).

Tip

To overload an operator simply means to define what an operator does when used with a specific type of object. In other words, when you overload the + operator for a Fraction class, you tell .NET what to do when your code adds two Fraction objects together.

For example, here's an operator method that adds support for the addition (+) operator:

Public ...