Inherit from data types

How to create a class which inherits from a data type, specifically from Char data type? I just wan't to add one property to it. If it's not possible, are there any other 开发者_运维知识库ways to accomplish this?

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I didn't think you could inherit from System types.

Remember an extension method can be only a Sub procedure or a Function procedure. You cannot define an extension property, field, or event.

Your options:

• Extension method (can only be a function or sub)
• A custom structure (use Reflector to make your own custom Char)
• A class that takes System.Char is input and allows you to store the Char and your extra property. You will need to implement your own IsLetter and the like.

Quick and dirty example (you may want to make this Static by placing it in a Module instead):

Class MyChar

  Sub New()
  End Sub
  Sub New(byval input As System.Char)
    Me.[Char] = input
  End Sub
  Sub New(byval input As String)
    Me.Parse(input)
  End Sub

  Public Property [Char] As System.Char
  Public Property ExtraProperty As String

  Public ReadOnly Property IsLetter As Boolean
    Get
        return Me.[Char].IsLetter(Me.[Char])
    End Get
  End Property

  Public Function Parse(ByVal input As String)
    If (input Is Nothing) Then
        Throw New ArgumentNullException("input")
    End If
    If (input.Length <> 1) Then
        Throw New FormatException("Need a single character only")
    End If
    Me.[Char] = input.Chars(0)
  End Function

End Class

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Deriving from System.Char would be madness and a useless effort. Extension methods to the rescue.