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

Here is an implementation combining Hans Passant's answer and Jon Skeet's answer.

It works even for millions of properties (i.e. no integer overflow exceptions) and is very fast (less than 20 ms to generate hash code for a class with 1,000,000 fields and barely measurable for a class with only 100 fields).

Here is the structure to handle the overflows:

Private Structure HashCodeNoOverflow
     Public Int64 As Int64
     Public Int32 As Int32
End Structure

And a simple GetHashCode function:

Public Overrides Function GetHashCode() As Integer

    Dim hashCode As HashCodeNoOverflow

    hashCode.Int64 = 17

    hashCode.Int64 = CLng(hashCode.Int32) * 23 + Field1.GetHashCode
    hashCode.Int64 = CLng(hashCode.Int32) * 23 + Field2.GetHashCode
    hashCode.Int64 = CLng(hashCode.Int32) * 23 + Field3.GetHashCode

    Return hashCode.Int32

End Function

Or if your prefer:

Public Overrides Function GetHashCode() As Integer

    Dim hashCode = New HashCodeNoOverflow With {.Int32 = 17}

    For Each field In Fields
        hashCode.Int64 = CLng(hashCode.Int32) * 23 + field.GetHashCode
    Next

    Return hashCode.Int32

End Function