Creating A Named Function Parameter Array

Question

Is it possible to create a routine in VB.NET with a name-based parameter array?

The WebMethod attribute built into the framework is used exactly this way:

  WebMethod(BufferResponse:=False)

Specifically, I'd like to use it in a class' constructor. I'd like something similar to this:

  New MyObject(id:=10,buffer:=True)

I'm not even sure what the terminology is for this kind of parameter list, so I can't even find it when searching.

score 2 · Answer 1 · answered Apr 21 '11 at 21:10

2

Are you trying to create an object from scratch or does there already exist a class definition already? If the class exists you can use either named parameters in the constructor with default parameters:

Public Class TestClass
    Public Property A As Integer
    Public Property B As Integer
    Public Sub New(Optional ByVal a As Integer = -1, Optional ByVal b As Integer = -1)
        Me.A = a
        Me.B = b
    End Sub
End Class

Dim Obj As New TestClass(b:=2)

There's also object initialization:

Dim Obj As New TestClass() With {.A = 2}

Or are you trying to create a generic object like in Javascript/JSON? Like:

var obj = new Object();
obj.MyProp = 27;

This type of syntax doesn't exist for VB

answered Apr 21 '11 at 21:10

Chris Haas

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The JavaScript dynamic `var obj = new Object(); obj.MyProp = 27;` is equivalent to the new dynamic [ExpandoObject](http://msdn.microsoft.com/en-us/library/system.dynamic.expandoobject.aspx) in .Net 4. `Dim obj = New ExpandoObject: obj.MyProp = 27`. Sadly it does [require Option Strict Off](http://stackoverflow.com/questions/3305275/net-4-0-framework-dynamic-features-in-vb-with-option-strict-on) in VB >:( – MarkJ Apr 22 '11 at 05:57
@MarkJ, never new that existed, thanks for the info! Too bad I can never use it, though, since I run with Option Strict On all the time. – Chris Haas Apr 22 '11 at 12:49

score 0 · Accepted Answer · answered Apr 22 '11 at 06:08

0

You don't need to do anything special in the definition of MyObject. Just go straight ahead and type New MyObject(id:=10,buffer:=True), assuming that the constructor has parameters called id and buffer. This means you can type the parameters in any order, you don't have to use the order in the declaration. See the VB manual.

Personally I think this named parameter style is a bit old-fashioned, and it will make it hard for other developers to read your code, unless they're old like me and remember VB6. The style was common in VB6 with optional parameters, but IMHO (and according to Microsoft) in VB.Net overloading is usually more elegant than optional parameters.

answered Apr 22 '11 at 06:08

MarkJ

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This is exactly what I was looking to do, I just didn't know it existed. I agree the an overloaded constructor would be better, but in this case I need 2 constructors that would have identical signatures. With named parameters, I am able to specify which one I want to specify in which scenario. – Justin Apr 22 '11 at 13:39
I think the compiler won't let you have 2 constructors with identical signatures? – MarkJ Apr 23 '11 at 08:26

Creating A Named Function Parameter Array

2 Answers2