VB dynamic parameters for functions - vb.net

Question

Is there any way to get the parameters of a function dynamic?
Like:
Function(text As String, If text = "yes" text2 As String)
End Function
So the second one just gets asked, when the first is filled or a certain value?
Optional is no way, cause for example the third needs to be filled when the second one is already.

Answer 1

No, you can't do that. But you might accomplish something similar via Currying.
Currying takes a function that needs multiple arguments, and converts into a set of functions that each need a single argument, where prior functions in the set return the next function in the set.
Where this will still be problematic for your situation is .Net likes strongly-typed delegates. If the initial function needs to return a method with one argument for any case, it must do that for all cases.
However, that doesn't mean it returns the same function. You can still vary which function is returned based on the initial input argument.
So instead of this:
Function test(text As String, a As String) As String
If text = "yes" Then
Return text & a
Else
Return a & text
End If
End Function
test("yes", "foo") ' produces "yesfoo"
test("no", "foo") ' produces "foono"
We have this:
Function test(text As String) As Func(Of String, String)
If text = "Yes" Then
Return Function(a) text & a
Else
Return Function(a) a & text
End If
End Function
test("yes")("foo") ' produces "yesfoo"
test("no")("foo") ' produces "foono"
This won't do exactly what you want; it still requires the additional argument or not in every situation. But it might give you enough new flexibility to accomplish your ultimate goal. For example, perhaps you could combine this with a closure, where you never use the additional argument, but in the case where you need it the additional value is still available. Exactly how this will look or whether it's really possible or helpful will depend on the details of what you're trying to accomplish beyond the simple test code in the question.

Answer 2

You could handle what to pass in the button code.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim paramValue As String
If MyTestText = "yes" Then
paramValue = TextBox2.Text
Else
paramValue = TextBox1.Text
End If
End Sub
Private Function SomeFunction(text As String) As String
Dim ReturnValue As String = ""
'your code here
Return ReturnValue
End Function
Or you could pass both values and test in your Function code
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim ReturnedValue = SomeFunction(TextBox1.Text, TextBox2.Text)
End Sub
Private Function SomeFunction(text1 As String, text2 As String) As String
Dim ReturnValue As String = ""
If MyTestText = "yes" Then
'process text2
Else
'process text1
End If
Return ReturnValue
End Function
I am sure there are other ways to handle this.