because of my project, learned something about VB.NET. and now by chance, find this stuff. it's pretty cool.
Visual Studio 2005
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.
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.
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