Value of type 'System.Func(Of String, String)' cannot be converted to 'System.Convert

Value of type 'System.Func(Of String, String)' cannot be converted to 'System.Converter(Of String, String)

Why? They are both effectively a function pointer (or delegate?) to a function that accept a string and return a string.

SO there has to be a way to make that thing work.

They're not the same. One has a type of System.Func(Of String, String) the second one is System.Converter(Of String, String).

Tell us more about what are you trying to do. (With the code, preferrably).

Looks to me both accept function (x) x

Error 1 Overload resolution failed because no accessible 'PerformATask' is most specific for these arguments:
'Public Sub PerformATask(filename As String, func As System.Func(Of String, String))': Not most specific.
'Public Sub PerformATask(filename As String, func As System.Converter(Of String, String))': Not most specific.

It's essentially the same thing yet not convertable to one or the other

vb.net Code:

Public Sub PerformATask(ByVal filename As String, ByVal func As System.Converter(Of String, String))
        Dim colBuffer = fileToStringCol(filename)
 
        colBuffer = colBuffer.ConvertAll(Of String)(func)
    End Sub
    Public Sub PerformATask(ByVal filename As String, ByVal func As System.Func(Of String, String))
        PerformATask(filename, Function(x) func(x))
    End Sub

It is still not quite clear to me what are you trying to do, but consider the following code:

vb Code:

Public Class Form1
    Private Delegate Function TestDelegate(ByVal StringParam As String) As String
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim d1 As TestDelegate = AddressOf MainImplementation
        Dim d2 As TestDelegate = AddressOf AlternativeImplementation
 
        Dim argument As String = "test"
 
        DoATask(d1, argument)
        DoATask(d2, argument)
    End Sub
 
    Private Function MainImplementation(ByVal param1 As String) As String
        Return param1 & "(main implementation)"
    End Function
 
    Private Function AlternativeImplementation(ByVal param1 As String) As String
        Return param1 & "(alternative implementation)"
    End Function
 
    Private Sub DoATask(ByVal method As TestDelegate, ByVal arg As String)
        MsgBox(method.Invoke(arg))
    End Sub
End Class

It uses two different implementations (Main and Alternative) and two delegates of the same type (TestDelegate)

In your code you're using two different delegates (even if they happen to have the same number of arguments and the same returned value).

You mean, a function delegate that have the same number of arguments and the same returned value are actually 2 different delegates?

Is delegate an object or a type anyway?

Let's examine this code:

vb.net Code:

Dim b = Function(x As String) x ' type of b is <function (string) as string> based on option infer (why the < and > anyway?)
        Dim c As System.Func(Of String, String) = b 'whatever type b is, sort of work with system.func and system.converter
        Dim d As System.Converter(Of String, String) = b 'whatever type b is, sort of work with system.func and system.converter
        Dim e As <function (string) as string> 'can't declare b type normally this is a compile error

How do we declare e as a delegate to a function that accepts a string and return a string without initializing it?

I mean we did that in Dim b = Function(x As String) x

This is another way to see the problem

function hello(f as WHAT?) as string
so that
dim g as system.converter(of string, string)=f works
and
dim h as system.converter(of string, string)=f works too

More like a type. In your case Func(Of String, String) is one delegate and Converter(Of String, String) - is another.

It's the same with interfaces.

vb Code:

Public Interface A
        Sub DoATask()
    End Interface
 
    Public Interface B
        Sub DoATask()
    End Interface

If one class implements interface A and another one implements Interface B they won't match

Dim b = Function(x As String) x

What is the type of b?