What does := mean in vb.net?

Question

We have this method call:

SendAck(AppData:=AppData, Status:=Status, StatusMessage:=StatusMessage, IsApplication:=IsApplication)

And here is the definition:

Private Sub SendAck(ByVal AppData As XDocument, ByVal Status As Boolean, ByVal StatusMessage As String, ByVal IsApplication As Boolean)

Why does the call have the parameters with the ":=". I'm just curious.

Answer 1

The ":=" in VB.Net is used to pass a function argument by name. The default is by position. It allows for parameters to be called in any order and determines the positioning based on name matches.

For example

Sub Example(ByVal param1 as Integer, ByVal param2 As Integer) 
  Console.WriteLine("{0} - {1}", param1, param2)
End Sub

Example(param2:=42, param1:=1) ' Prints "1 - 42"
Example(42, 1)                 ' Prints "42 - 1"

Answer 2

That syntax is using named arguments; Specifying the names of the parameters being set before the := then the value after. Doing that can enable you to skip parameters or do them in different order.