IEnumerable. An IEnumerable collection contains elements. We use the For-Each loop in VB.NET to loop over these elements. Lists and arrays implement this interface.
Interface benefits. We can use Extensions, such as ToList, on an IEnumerable type. Query expressions, part of LINQ, can be done with IEnumerables as well.
Important We can act upon a List and an array with the same code, by using the IEnumerable interface implemented by both types.
Module Module1
Sub Main()
' Step 1: create a List and String array.
Dim list1 As List(Of String) = New List(Of String)
list1.Add("one")
list1.Add("two")
list1.Add("three")
Dim array1(2) As String
array1(0) = "ONE"
array1(1) = "TWO"
array1(2) = "THREE"' Step 2: pass both to the Display sub.
Display(list1)
Display(array1)
End Sub
Sub Display(ByVal argument As IEnumerable(Of String))
' Step 3: loop over IEnumerable.For Each value As String In argument
Console.WriteLine("Value: {0}", value)
Next
Console.WriteLine()
End Sub
End ModuleValue: one
Value: two
Value: three
Value: ONE
Value: TWO
Value: THREE
Example 2. IEnumerable has other uses. Many Extension methods that act upon IEnumerable are implemented. These are available in all VB.NET programs based on recent .NET Frameworks.
Here We employ the ToList extension. This converts any IEnumerable type into a List. The element type remains the same.
Detail In this example, we implicitly cast the array into an IEnumerable reference. This step is not required.
Note We use this statement to show how the array is an IEnumerable instance, as well as an array.
Module Module1
Sub Main()
' An array.
' ... This implements IEnumerable.
Dim array1() As String = {"cat", "dog", "mouse"}
' Cast the array to IEnumerable reference.
Dim reference1 As IEnumerable(Of String) = array1
' Use an extension method on IEnumerable.
Dim list1 As List(Of String) = reference1.ToList()
' Display result.
Console.WriteLine(list1.Count)
End Sub
End Module3
Discussion. The IEnumerable interface is a critical abstraction in .NET. Many Functions are built upon this abstraction. Even the For-Each loop, a core construct, directly uses IEnumerable.
Tip In most programs, we will not need to implement IEnumerable ourselves. This is possible, but is not covered here.
Detail A thorough understanding of how to use IEnumerable on built-in types, including Lists and arrays, often has more benefit.
Summary. We explored the IEnumerable type in VB.NET. This interface is needed for the For-Each loop. It can be used to act upon arrays, Lists and many other collections with a unified code path.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Apr 22, 2023 (rewrite).