Does VB.NET have anonymous functions?

Question

From what I can find on google, VB.NET only has one-statement lambdas, and not multi-statement anonymous functions. However, all the articles I read were talking about old versions of VB.NET, I couldn't find anything more recent than vs2008 beta 1 or 2.

So the question: How can I do this in VB.NET?

C# code:

private void HandleErrors( Action codeBlock ){
    try{
        codeBlock();
    }catch(Exception e){
        //log exception, etc
    }
}

HandleErrors(() => {
    var x = foo();
    x.DoStuff();
    etc
});

Healy

Answer 1

It does in VB10:

Dim food = New With {
    .ID = 1,
    .Name = "Carrot",
    .Type = (
        Function(name As String)
            If String.IsNullOrEmpty(name) Then Return String.Empty

            Select Case name.ToLower()
                Case "apple", "tomato": Return "Fruit"
                Case "potato": Return "Vegetable"
            End Select

            Return "Meat"
        End Function
    )(.Name)
}
Dim type = food.Type

Or, corresponding to your code:

Sub HandleErrors(codeBlock As Action)
    Try
        codeBlock()
    Catch e As Exception
        ' log exception, etc.
    End Try
End Sub

HandleErrors(Sub()
        Dim x = foo()
        x.DoStuff()
        ' etc.
    End Sub)

Cassel

great example ... though I didn't realize carrots were meat :) – Transferase

carrots: try the only orange meat! – Zambrano

Answer 2

Visual Basic .NET has only lambda expressions.

It does not support 'anonymous delegates" in the current version, though it will (and on multiple lines at that) in VS2010.

Right now the only option is to declare your method somewhere and pass it with the Addressof operator.

Norwood

unfortunately this is a big gaping hole I think. I can't wait for this to be included. On the other hand, they did a nice job on the query syntax XML litterals and LinqToXML support... – Norwood

Here is a good article from cOdE mag the talks about anonymous methods and lambda expressions code-magazine.com/Article.aspx?quickid=0809081 – Undone

Answer 3

VB9 has only single-line anonymous functions. We're adding full statement and multi-line lambdas in VB10.

Colostrum

Answer 4

in this example I have a list of operations but only want to find one from a list (of T) where the IDs match:

Return operations.Find(Function(p) p.OperationID = operationID)

operationID is a local variable passed in to the method and operations is a generic list.

Inductive

Answer 5

Anonymous isn't a delegate or function it's a strong dynamical type

you can use generic functions

Sub Main()
      Dim PersonDynamicType = AnonyFunc(New With {.Name = "david", .Family = "Fisher"})
      Console.Write(PersonDynamicType.Name)
End Sub

Function AnonyFunc(Of t)(v As t) As t
      Return v
End Function

Runt

If it's strongly typed, then in what way is it dynamic? But an anonymous type is just that -- a type which doesn't have a name in the source code of the program. The compiler assigns it a name, but you cannot directly use this name from code. – Brassard

Answer 6

This is inaccurate. VB.NET does in fact have anonymous methods. Here is an example:

Private Function JsonToObject(Of T)(Value As String) As T
    Dim JavaScriptSerializer As New System.Web.Script.Serialization.JavaScriptSerializer()
    Return JavaScriptSerializer.Deserialize(Of T)(Value)
End Function

Dim People As Generic.List(Of Person) = JsonToObject(Of Generic.List(Of Person))(Json)

Gallon

It's called JsonToObject. Sorry couldn't help myself :P – Minnieminnnie