Module Multiple Return Values Property Sub

Function

A Function returns a value. It uses a special syntax form in the VB.NET language. The Function optionally accepts one or more parameters—these are called formal parameters.

A Function is part of a Module, Class or Structure. A Function is called from other Functions, Subs or Properties. It can be reused throughout a program.

First example

This program shows the Function keyword. We provide an Area Function: this Function receives a radius. It returns a Double that is the area of a circle with that radius.

Detail Area receives one formal parameter of type Double. Specifying the type of the parameter is optional but advised.

Return The Function returns a value of type Double. After the formal parameter list, the keywords "As Double" indicate the return type.

Module Module1

    ''' <summary>
    ''' Get area of a circle with specified radius.
    ''' </summary>
    Function Area(ByVal radius As Double) As Double
        Return Math.PI * Math.Pow(radius, 2)
    End Function

    Sub Main()
        Dim a As Double = Area(4.0)
        Console.WriteLine(a)
    End Sub

End Module
50.2654824574367

No argument

A Function must return a value—otherwise we must use a Subroutine. But a Function does not need to receive a value—it can have an empty parameter list.

Module Module1

    Function GetID() As Integer
        ' This function receives no arguments.
        Return 100
    End Function

    Sub Main()
        ' Use GetID function.
        Console.WriteLine(GetID())
    End Sub

End Module
100

Functions, Properties

What is the difference between a Function and a Property? A Property is a type of Function. The Get part of a Property can be implemented as a Function.

Info Properties are meant to replace getters and setters. If you have a Sub that sets a value, it can be changed to be a Property.

Tip At the level of the implementation, Properties are similar to Functions and Subs.

And If you want to, you can change all Properties on your types to Functions and Subs.

But On existing types, such as those in .NET, you must use the Property syntax if the member is a Property.

Module Module1

    ReadOnly Property ID As Integer
        Get
            Return 100
        End Get
    End Property

    Function GetID() As Integer
        Return 100
    End Function

    Sub Main()
        ' Use property and function.
        Console.WriteLine("PROPERTY: {0}", ID)
        Console.WriteLine("FUNCTION: {0}", GetID())
    End Sub

End ModulePROPERTY: 100
FUNCTION: 100

Return values

A Function can only return one value. But if this value is a class or Structure, it can return many values in this step. ByRef can be used to set output parameters.

A summary

Unlike a Sub, a Function returns a value. We must return this value—if we have no return value, we need to use a Sub instead. We can assign to the result of a Function.