Hi all,

why in the world would this fail ( throw an exception)


        Dim str As String = ""

        MsgBox(IIf(IsNumeric(str), Convert.ToInt32(str).ToString, str))

Why does it try to evaluate the true part when the condition is false.

Or am i missing something here.

Thanks in advance.

Because it's a function.

doh!.

Thanks

I thought it was more like a  ?: operator.. I forgot it was  a
function..
Thanks again

Parez,

Not only however mainly because its behaviour is mostly advices to avoid the
IIF in VBNet.

Cor

Parez,
As Cor suggests a number of developers discourage its use, as it does
evaluate both of its parameters, which may have undesired side effects as
you found out. Plus it is not Option Strict On friendly, as it accepts
Object as its parameters & returns an Object. Accepting & returning Object
means that it will box value parameters, which is a slight performance hit &
causes extra pressure on the GC. Returning object means you need to cast to
the specific type, leading to "awkward" code.

In places where it does make sense to use the IIf function, I normally use
my Generic IIf function. Being Generic removes the "boxing penalty" and the
"awkward" code factor. However its still a function ;-)

http://www.tsbradley.net/Cookbook/Generics/genericIIf.aspx



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I meant it returns str. but it also tries to evaluate the true part

It's similiar to If xxx and yyy then...both are evaluated whereas in If xxx
andalso yyy then... only the first xxx is evaluated if it's false...yyy is
only evaluated if xxx is true. 

If you pass parameters to a function, all are evaluated to their final value.
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