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By Jim Counts
In Perl (and other languages) a conditional ternary operator can be expressed like this:
my $foo = $bar == $buz ? $cat : $dog;
Is there a similar operator in VB.NET?
Depends upon the version. The If operator in VB.NET 2008 is a ternary operator (as well as a null coalescence operator). This was just introduced, prior to 2008 this was not available. Here's some more info: Visual Basic If announcement
Dim foo as String = If(bar = buz, cat, dog)
Prior to 2008 it was IIf, which worked almost identically to the If operator described in your link.
...with the important difference that Iif(), being a function, always evaluated both the consequent and the alternative, while the new If only evaluates one of them.
what is it means ? If (condition,true-part,false-part). may i rite ?
@VeeKayBee Yes. You're right.
I'm a huge C guy, but I find this syntax cleaner than the traditional ternary operator.
Another important distinction: Iif always returns an object of type Object, whereas If(bool, obj, obj) allows for type-checking with option strict on. (Dim var As Integer = Iif(true, 1, 2) won't compile with option strict on because you could just as easily write Dim var As Integer = Iif(true, new Object(), new Object()). You CAN write Dim var As Integer = If(true, 1, 2) with option strict on though, because it'll check the type returned.)
If(bool, obj, obj)
Dim var As Integer = Iif(true, 1, 2)
Dim var As Integer = Iif(true, new Object(), new Object())
Dim var As Integer = If(true, 1, 2)
If() is the closest equivalent but beware of implicit conversions going on if you have set "Option Strict off"
For example, if your not careful you may be tempted to try something like:
Dim foo As Integer? = If( someTrueExpression, Nothing, 2)
Will give "foo" a value of 0!
I think the '?' operator equivalent in C# would instead fail compilation
Just for completeness, the better way to write that expression is Dim foo As Integer? = If( someTrueExpression, New Integer?, 2).
Dim foo As Integer? = If( someTrueExpression, New Integer?, 2)
Note that this also happen with Option Strict On. The reason is that Nothing in VB.NET is equivalent to C#'s default(T) rather than to null.
Option Strict On
And for anyone puzzled by Integer? it means it's nullable - see stackoverflow.com/questions/3628757/make-an-integer-null
For anyone getting stuck on implicit conversion for nullable types - see this answer as to why and this answer for a workaround which casts the argument before returning (CType(Nothing, DateTime?).
iif has always been available in VB, even in VB6.
Dim foo as String = iif(bar = buz, cat, dog)
It is not a true operator, as such, but a function in the Microsoft.VisualBasic namespace.
Iif is only close to a ternary operator though - which means you couldn't use it in every condition that you would an If Then Else (or ternary operator). For example, Value = Iif(1 = 1, 0, 1/0) would blow up, but Value = If(1 = 1, 0, 1/0) would not ...
VB doesn't support Short Circuit evaluation (except for the AndAlso operator), so VB programmers don't really expect that they can safely evaluate half an operation. But point taken, also iif is a hack function that was put in for backward compatibility otherwise it would be a real operator.
Nice to categorize all VB programmers ;-) And there is also IsNot and OrElse to shortcut, so VB does indeed support Short Circuit Evaluation.
Iif is a regular method call and evaluates all parameters. It is not ternary. Se dotnetslackers.com/VB_NET/…
As I stated, it is NOT a true operator, and vb6 doesn't support short circuit evaluation so it always evaluates all operations on line anyway.
Method IIf is a part of Microsoft.VisualBasic namespace, that is not compatible with other .NET languages. So better practice is use If() mehod.