Overriding GetHashCode in VB without checked/unchecked keyword support?

Question

So I\'m trying to figure out how to correctly override GetHashCode() in VB for a large number of custom objects. A bit of searching leads me to this wonderful

Answer 1

Use Long to avoid the overflow:

Dim hash As Long = 17
'' etc..
Return CInt(hash And &H7fffffffL)

The And operator ensures no overflow exception is thrown. This however does lose one bit of "precision" in the computed hash code, the result is always positive. VB.NET has no built-in function to avoid it, but you can use a trick:

Imports System.Runtime.InteropServices

Module NoOverflows
    Public Function LongToInteger(ByVal value As Long) As Integer
        Dim cast As Caster
        cast.LongValue = value
        Return cast.IntValue
    End Function

     _
    Private Structure Caster
         Public LongValue As Long
         Public IntValue As Integer
    End Structure
End Module

Now you can write:

Dim hash As Long = 17
'' etc..
Return NoOverflows.LongToInteger(hash)