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I am using a function to compare over 100 variables inside of classes to each other an am curious if one method of comparing multiple condition statements is more efficient than another. I am currently considering one of these methods. I think the 'single If using And/Or' looks the cleanest but performance is more important. (my code is VB.Net)

Multiple ElseIf

If Not ClassA.num = ClassB.num Then
    Return False
ElseIf Not ClassA.str = ClassB.str Then
    Return False
Else : Return True
End If

Single If using And/Or

If Not ClassA.num = ClassB.num Or
   Not ClassA.str = ClassB.str Then
       Return False
Else : Return True
End If

Nested If

If ClassA.num = ClassB.num Then
    If ClassA.str = ClassB.str Then
        Return True
    End If
End If
Return False

Edit: Changed second code snippet from And to Or

Edit 2: Changed third snippet from If Not to If

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You will want to read Description of "short-circuit" evaluation in Visual Basic –  MichaelT Feb 6 '14 at 20:52
the three examples are not equivalent; the first one returns false when ClassA.num != ClassB.num OR ClassA.str != ClassB.str –  Steven A. Lowe Feb 6 '14 at 22:39
Rule 1) of Optimization - You Can not tell without profiling. My experience of optimizers is that usually they do a much better job than me at this kind of stuff. –  mattnz Feb 7 '14 at 2:12
@Wayne: now the third snippet doesn't match the other two ;) –  Steven A. Lowe Feb 11 '14 at 16:57
@Steven: Okay... this time they should all match (if anyone was wondering: the first snippet was how I wrote my original code, but I changed it to the second snippet using OrElse statements) –  Wayne Feb 11 '14 at 17:58

1 Answer 1

up vote 2 down vote accepted

I don't think it gets any more efficient than short-circuit evaluation for real trivial chains like this:

Return ClassA.intVariable = ClassB.intVariable AndAlso ClassA.longVariable = _
        ClassB.longVariable AndAlso ClassA.str = ClassB.str

Notice how AndAlso is used, not And. Also shorter, quicker-to-compare stuff is mentioned (and evaluated) first, with longer, slower-to-compare stuff further in the back.

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Most of my schooling was in C# so I did not know that in VB.Net using And / Or was not short-circuiting. –  Wayne Feb 6 '14 at 21:10

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