What is the VB.NET equivalent of the C# "is" keyword?

Try the following

if TypeOf x Is IFoo Then 
  ...

Like this:

If TypeOf x Is IFoo Then

The direct translation is:

If TypeOf x Is IFoo Then
    ...
End If

But (to answer your second question) if the original code was better written as

var y = x as IFoo;
if (y != null)
{
   ... something referencing y rather than (IFoo)x ...
}

Then, yes,

Dim y = TryCast(x, IFoo)
If y IsNot Nothing Then
   ... something referencing y rather than CType or DirectCast (x, IFoo)
End If

is better.

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