Hidden Features of VB.NET?

Question

I have learned quite a bit browsing through Hidden Features of C# and was surprised when I couldn't find something similar for VB.NET.

So what are some of its hidden or lesser known features?

Answer 1

Oh! and don't forget XML Literals.

Dim contact2 = _
        <contact>
          <name>Patrick Hines</name>
          <%= From p In phoneNumbers2 _
            Select <phone type=<%= p.Type %>><%= p.Number %></phone> _
          %>
        </contact>

Answer 2

Object initialization is in there too!

Dim x as New MyClass With {.Prop1 = foo, .Prop2 = bar}

Answer 3

Passing parameters by name and, so reordering them

Sub MyFunc(Optional msg as String= "", Optional displayOrder As integer = 0)

    'Do stuff

End function

Usage:

Module Module1

    Sub Main()

        MyFunc() 'No params specified

    End Sub

End Module

Can also be called using the ":=" parameter specification in any order:

MyFunc(displayOrder:=10, msg:="mystring")

Answer 4

If conditional and coalesce operator

I don't know how hidden you'd call it, but the Iif([expression],[value if true],[value if false]) As Object function could count.

It's not so much hidden as deprecated! VB 9 has the If operator which is much better and works exactly as C#'s conditional and coalesce operator (depending on what you want):

Dim x = If(a = b, c, d)

Dim hello As String = Nothing
Dim y = If(hello, "World")

---

Edited to show another example:

This will work with If(), but cause an exception with IIf()

Dim x = If(b<>0,a/b,0)

Answer 5

One major time saver I use all the time is the With keyword:

With ReallyLongClassName
    .Property1 = Value1
    .Property2 = Value2
    ...
End With

I just don't like typing more than I have to!

Answer 6

I just found an article talking about the "!" operator, also know as the "dictionary lookup operator". Here's an excerpt from the article at: http://panopticoncentral.net/articles/902.aspx

The technical name for the ! operator is the "dictionary lookup operator." A dictionary is any collection type that is indexed by a key rather than a number, just like the way that the entries in an English dictionary are indexed by the word you want the definition of. The most common example of a dictionary type is the System.Collections.Hashtable, which allows you to add (key, value) pairs into the hashtable and then retrieve values using the keys. For example, the following code adds three entries to a hashtable, and looks one of them up using the key "Pork".

Dim Table As Hashtable = New Hashtable
Table("Orange") = "A fruit"
Table("Broccoli") = "A vegetable"
Table("Pork") = "A meat" 
Console.WriteLine(Table("Pork"))

The ! operator can be used to look up values from any dictionary type that indexes its values using strings. The identifier after the ! is used as the key in the lookup operation. So the above code could instead have been written:

Dim Table As Hashtable = New Hashtable
Table!Orange = "A fruit"
Table!Broccoli = "A vegetable"
Table!Pork = "A meat"
Console.WriteLine(Table!Pork)

The second example is completely equivalent to the first, but just looks a lot nicer, at least to my eyes. I find that there are a lot of places where ! can be used, especially when it comes to XML and the web, where there are just tons of collections that are indexed by string. One unfortunate limitation is that the thing following the ! still has to be a valid identifier, so if the string you want to use as a key has some invalid identifier character in it, you can't use the ! operator. (You can't, for example, say "Table!AB$CD = 5" because $ isn't legal in identifiers.) In VB6 and before, you could use brackets to escape invalid identifiers (i.e. "Table![AB$CD]"), but when we started using brackets to escape keywords, we lost the ability to do that. In most cases, however, this isn't too much of a limitation.

To get really technical, x!y works if x has a default property that takes a String or Object as a parameter. In that case, x!y is changed into x.DefaultProperty("y"). An interesting side note is that there is a special rule in the lexical grammar of the language to make this all work. The ! character is also used as a type character in the language, and type characters are eaten before operators. So without a special rule, x!y would be scanned as "x! y" instead of "x ! y". Fortunately, since there is no place in the language where two identifiers in a row are valid, we just introduced the rule that if the next character after the ! is the start of an identifier, we consider the ! to be an operator and not a type character.