Is there a conditional ternary operator in VB.NET?
Solution 1
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
Example:
Dim foo as String = If(bar = buz, cat, dog)
[EDIT]
Prior to 2008 it was IIf
, which worked almost identically to the If
operator described Above.
Example:
Dim foo as String = IIf(bar = buz, cat, dog)
Solution 2
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.
Solution 3
If()
is the closest equivalent, but beware of implicit conversions going on if you have set Option Strict off
.
For example, if you're 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.
Solution 4
Just for the record, here is the difference between If and IIf:
IIf(condition, true-part, false-part):
- This is the old VB6/VBA Function
- The function always returns an Object type, so if you want to use the methods or properties of the chosen object, you have to re-cast it with DirectCast or CType or the Convert.* Functions to its original type
- Because of this, if true-part and false-part are of different types there is no matter, the result is just an object anyway
If(condition, true-part, false-part):
- This is the new VB.NET Function
- The result type is the type of the chosen part, true-part or false-part
- This doesn't work, if Strict Mode is switched on and the two parts are of different types. In Strict Mode they have to be of the same type, otherwise you will get an Exception
- If you really need to have two parts of different types, switch off Strict Mode (or use IIf)
- I didn't try so far if Strict Mode allows objects of different type but inherited from the same base or implementing the same Interface. The Microsoft documentation isn't quite helpful about this issue. Maybe somebody here knows it.
Comments
-
Jim Counts over 2 years
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?
-
Greg Hewgill about 15 years...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.
-
Beep beep about 15 yearsIif 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 ...
-
Kris Erickson about 15 yearsVB 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.
-
HardCode about 15 yearsNice to categorize all VB programmers ;-) And there is also IsNot and OrElse to shortcut, so VB does indeed support Short Circuit Evaluation.
-
kbvishnu about 12 yearswhat is it means ? If (condition,true-part,false-part). may i rite ?
-
LosManos over 11 yearsIif is a regular method call and evaluates all parameters. It is not ternary. Se dotnetslackers.com/VB_NET/…
-
Kris Erickson over 11 yearsAs 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.
-
Mark Hurd about 9 yearsJust for completeness, the better way to write that expression is
Dim foo As Integer? = If( someTrueExpression, New Integer?, 2)
. -
crush about 9 yearsI'm a huge C guy, but I find this syntax cleaner than the traditional ternary operator.
-
Joseph Nields almost 9 yearsAnother important distinction:
Iif
always returns an object of typeObject
, whereasIf(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 writeDim var As Integer = Iif(true, new Object(), new Object())
. You CAN writeDim var As Integer = If(true, 1, 2)
with option strict on though, because it'll check the type returned.) -
Can Sahin over 8 yearsNote that this also happen with
Option Strict On
. The reason is thatNothing
in VB.NET is equivalent to C#'sdefault(T)
rather than tonull
. -
AjV Jsy almost 8 yearsAnd for anyone puzzled by
Integer?
it means it's nullable - see stackoverflow.com/questions/3628757/make-an-integer-null -
KyleMit about 7 yearsFor 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?
). -
Aave over 5 yearsMethod IIf is a part of Microsoft.VisualBasic namespace, that is not compatible with other .NET languages. So better practice is use If() mehod.
-
jmoreno about 5 years@Aave: the namespace certainly is compatible with other languages, this particular function has always been rather pointless, but that doesn’t mean everything in the namespace is po8ntless or can only be used with vb.
-
Eli Fry about 2 yearsMy answer adds to the existing, it is not reflected in the accepted answer and can be simpler if this is the use case they are using it for. Unfortunately I don't have enough reputation to comment under that post to share my update.