Operator Overloading in Visual Basic

Introduction

In this article, you will learn about Operator overloading in Visual Basic.

What Are Operators?

Here is a complete list of Operators available in Visual Basic.

What Is Operator Overloading?

Operator overloading takes place where different operators have different implementations, depending on their arguments.

This article is a very good guideline on Operators and Operator Overloading.

Today's Project

Create a Console application and add a new class to it. You may name the class anything you like, but keep in mind that my object names might differ from yours. Add the following code into your newly created class.

Add the following member variables to your class:

   Private X As Integer
   Private Y As Integer

Add the constructor:

   Sub New(ByVal x2 As Integer, _
      ByVal y2 As Integer)

      X = x2
      Y = y2

   End Sub

In the New sub, or the Constructor, I have added two arguments that we will supply to the calling class. Whatever values we supply here will be used in calculations with the new overridden operators.

The Plus Operator

   Public Shared Operator +(ByVal Param1 As Operators, _
                            ByVal Param2 As Operators) _
                               As Operators
      Return New Operators(Param1.X + Param2.X, _
                           Param1.Y + Param2.Y)
   End Operator

In the preceding code, the plus operator gets overridden to calculate Param1.X + Param2.X as well as Param1.Y + Param2.Y, thus providing a new skeleton for the plus operation.

The Minus Operator

   Public Shared Operator -(ByVal Param1 As Operators) _
         As Operators
      Return New Operators(-Param1.X, -Param1.Y)
   End Operator

Multiply

   Public Shared Operator *(ByVal Param1 As Operators, _
                            ByVal Param2 As Integer) _
                               As Integer
      Return (Param1.X * Param2) + (Param1.Y * Param2)
   End Operator

Greater Than and Less Than Operators

   Public Shared Operator >(ByVal Param1 As Operators, _
                            ByVal Param2 As Operators) _
                               As Boolean
      Return (Param1.X + Param1.Y) > (Param2.X + Param2.Y)
   End Operator

   Public Shared Operator <(ByVal Param1 As Operators, _
                            ByVal Param2 As Operators) _
                               As Boolean
      Return Not Param1 > Param2
   End Operator

Narrowing and Widening Operator(s)

   Public Shared Narrowing Operator CType(ByVal Param1 _
         As Operators) As Point
      Return New Point(Param1.X, Param1.Y)
   End Operator

A widening conversion changes a value to a data type that can allow for any possible value of the original data. Widening conversions preserve the source value but can change its representation. This occurs if you convert from an integral type to Decimal, or from Char to String.

A narrowing conversion changes a value to a data type that might not be able to hold some of the possible values. For example, a fractional value is rounded when it is converted to an integral type, and a numeric type being converted to Boolean is reduced to either True or False.

Here is more information on the Narrowing and Widening operators.

Putting It All Together

Add the following into a newly added Module.

Module Module1

   Sub Main()
      Dim bool As Boolean
      Dim int As Integer
      Dim Var1 As New Operators(4, 5)
      Dim Var2 As New Operators(2, -1)

      Var1 = Var1 + Var2                    'Calls 1
      Console.WriteLine(Var1)

      Var1 = -Var1                          'Calls 2
      Console.WriteLine(Var1)

      int = Var2 * 4                        'Calls 3
      Console.WriteLine(int)

      Dim pt As Point = CType(Var1, Point)  'Calls 4
      Console.WriteLine(pt.ToString)

      bool = Var1 > Var2                    'Calls 5
      Console.WriteLine(bool)

   End Sub

End Module

Conclusion

There is still a lot learn about Operator overloading. This little article's aim was just to show you how it can be done; obviously, the onus now rests on your shoulders to continue exploring this topic.



About the Author

Hannes DuPreez

Hannes du Preez is a Microsoft MVP for Visual Basic for the eighth consecutive year. He loves technology and loves Visual Basic. He has a lot of experience in .NET and loves to share his love, pain and musings about Visual Basic

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