Is there a conditional ternary operator in VB.NET?

Question

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?

Answer 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)

Answer 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.

Answer 3

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

Answer 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.