Question

I have got this error
No default member found for type 'VB$AnonymousDelegate_0(Of SqlDataReader,String,Object)'.

My Code is below

dsBranch.Tables.Add(GetDataTableFromSQLReader(dr, "")) – Calling

Private Function GetDataTableFromSQLDataReader(ByVal dr As SqlDataReader, ByVal TableName As String)
    Dim dt As New DataTable(TableName)
    dt.Load(dr)
    Return dt
End Function
Dim GetDataTableFromSQLReader = Function(dr As SqlDataReader, TableName As String) GetDataTableFromSQLDataReader(dr, TableName)

Answer 1

Imports System.Data
Imports System.Data.SqlClient

Public Class NoDefaultMemberFoundError

    ' Added "As DataTable"
    Private Function GetDataTableFromSQLDataReader(ByVal dr As SqlDataReader, _
                                                   ByVal TableName As String) As DataTable
        Dim dt As New DataTable(TableName)
        dt.Load(dr)
        Return dt
    End Function

    ' This is how it has to be declared
    Dim GetDataTableFromSQLReader As Func(Of SqlDataReader, String, DataTable) = _
                       Function(dr, TableName) GetDataTableFromSQLDataReader(dr, TableName)

    Sub Test()
        Dim dsBranch As DataSet = Nothing
        Dim dr As SqlDataReader = Nothing

        dsBranch.Tables.Add(GetDataTableFromSQLReader(dr, ""))
    End Sub
End Class

You should set the Option Strict to On. It would help you to declare the correct types. For instance, your Function had no return type declared. This was probably the main source of the error.

Your Lambda assignment was also not correct. Lambda expressions always have to be assigned to a concrete type. This enables the compiler to infer their exact signature.

---

EDIT (explanation of delegates and lambda expressions):

With

Dim GetDataTableFromSQLReader As Func(Of SqlDataReader, String, DataTable)

you define a variable, which can hold a function, or more precisely its address, in a specialized class called a ‘delegate’. In terms of .NET this variable is a delegate which refers to a method (unless it is Nothing). According to the declaration above, this function must accept one parameter of type SqlDataReader and one of type String. The return value must be of type DataTable.

You can assign any function, which has this requested signature to the variable:

GetDataTableFromSQLReader = AddressOf GetDataTableFromSQLDataReader

is a valid assignment. (I could have simplified the example in my original answer this way.) Now you can use the variable as if it was a function:

Dim DataTable dt = GetDataTableFromSQLReader(dr, "")

In reality this calls the function that was assigned to it, namely GetDataTableFromSQLDataReader. This makes sense, if we want to get the data tables in different ways. We could assign another function, say GetDataTableInADifferentWay to our variable. The call GetDataTableFromSQLReader(dr, "") would then call this other function without the need of having an If-Then-Else-statement when we call it.

Now, to the lambda expressions with a detour over delegates. Let us take an example that is more suitable. We want to print a table with function values:

Public Sub PrintFunction()
    For Dim x As Double = 1 To 10
        Console.WriteLine("x = {0}, f(x) = {1}", x, x*x)
    Next
End Sub

As you can see, we print the squares of 1 to 10. However, what about printing other functions? We would have to change our PrintFunction each time we need to print another function. Here delegates come into the game. Let us change the declaration to

Public Sub PrintFunction(Func(Of Double, Double) f)
    For Dim x As Double = 1 To 10
        Console.WriteLine("x = {0}, f(x) = {1}", x, f(x))
    Next
End Sub

Now let us declare a square function and a reciprocal function

Public Function Square(x As Double) As Double
    Return x*x
End Function

Public Function Reciprocal(x As Double) As Double
    Return 1 / x
End Function

Now we can print two different value tables with

PrintFunction(AddressOf Square)
PrintFunction(AddressOf Reciprocal)

We have not used lambda expressions yet. They are simply a very concise way of declaring delegates (or functions, if you prefer) on the fly. Instead of declaring a square and a reciprocal function, we can print the tables like this:

PrintFunction(Function(x) x*x)
PrintFunction(Function(x) 1 / x)