How to: Define a Conversion Operator [msdn]

because of my project, learned something about VB.NET. and now by chance, find this stuff. it's pretty cool.

Visual Studio 2005

Other Versions

 

If you have defined a class or structure, you can define a type conversion operator between the type of your class or structure and another data type (such as Integer, Double, or String).

Define the type conversion as a CType Function procedure within the class or structure. All conversion procedures must be Public Shared, and each one must specify either Widening or Narrowing.

Defining an operator on a class or structure is also called overloading the operator.

Example

The following example defines conversion operators between a structure called digit and a Byte.

VB

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JScript

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Public Structure digit

Private dig As Byte

Public Sub New(ByVal b As Byte)

If (b < 0 OrElse b > 9) Then Throw New _

System.ArgumentException("Argument outside range for Byte")

Me.dig = b

End Sub

Public Shared Widening Operator CType(ByVal d As digit) As Byte

Return d.dig

End Operator

Public Shared Narrowing Operator CType(ByVal b As Byte) As digit

Return New digit(b)

End Operator

End Structure

You can test the structure digit with the following code.

VB

C#

C++

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Public Sub consumeDigit()

Dim d1 As New digit(4)

Dim d2 As New digit(7)

Dim d3 As digit = CType(CByte(3), digit)

Dim s As String = "Initial 4 generates " & CStr(CType(d1, Byte)) _

& vbCrLf & "Initial 7 generates " & CStr(CType(d2, Byte)) _

& vbCrLf & "Converted 3 generates " & CStr(CType(d3, Byte))

Try

Dim d4 As digit

d4 = CType(CType(d1, Byte) + CType(d2, Byte), digit)

Catch e4 As System.Exception

s &= vbCrLf & "4 + 7 generates " & """" & e4.Message & """"

End Try

Try

Dim d5 As digit = CType(CByte(10), digit)

Catch e5 As System.Exception

s &= vbCrLf & "Initial 10 generates " & """" & e5.Message & """"

End Try

MsgBox(s)

End Sub