Question

I saw this in some vb.net source code:

Dim sTest As String = "" & drTest("column")

I was told that if drTest(“column”) is nothing, then sTest will be assigned “”, so it is in effect doing:

Dim sTest As String = If("",Nothing,drTest("column"))

What is the downside of doing it the first way I showed?

What is the difference between using If and IIf?

Answer 1

If is the ternary conditional operator.

What is the difference between using If and IIf?

IIf is an ordinary function that is implemented approximately as follows:

Function If(Of T)(condition As Boolean, ifTrue As T, ifFalse As T)
    If condition Then Return ifTrue
    Return ifFalse
End Function

This means that no matter the value of condition, both its other arguments are always evaluated. This doesn’t happen with the If operator.

But your code is actually doing something completely different:

Dim sTest As String = If("",Nothing,drTest("column"))

This makes no sense and shouldn’t even compile (or at least give a warning). Your first code is fine – it works always and there is no downside. It’s not clear what the second code is even trying to achieve.