Can I implement yield return for IEnumerable functions in VB.NET? [duplicate]

This question already has answers here: Closed 10 years ago.

Possible Duplicate:

Yield In VB.NET

In C#, when writing a function that returns an IEnumerble<>, you can use yield return to return a single item of the enumeration and yield break; to signify no remaining items. What is the VB.NET syntax for doing the same thing?

An example from the NerdDinner code:

public IEnumerable<RuleViolation> GetRuleViolations() {

   if (String.IsNullOrEmpty(Title))
       yield return new RuleViolation("Title required","Title");

   if (String.IsNullOrEmpty(Description))
       yield return new RuleViolation("Description required","Description");

   if (String.IsNullOrEmpty(HostedBy))
       yield return new RuleViolation("HostedBy required", "HostedBy");

   if (String.IsNullOrEmpty(Address))
       yield return new RuleViolation("Address required", "Address");

   if (String.IsNullOrEmpty(Country))
       yield return new RuleViolation("Country required", "Country");

   if (String.IsNullOrEmpty(ContactPhone))
       yield return new RuleViolation("Phone# required", "ContactPhone");

   if (!PhoneValidator.开发者_C百科IsValidNumber(ContactPhone, Country))
       yield return new RuleViolation("Phone# does not match country", "ContactPhone");

   yield break;
}

This convert C# to VB.NET tool gives a "YieldStatement is unsupported" error.

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There is currently no equivalent to C#'s yield return in VB.Net from a language syntax level.

However there was a recent write up in MSDN magazine by Bill McCarthy on how to implement a similar pattern in VB.Net 9.0

• http://visualstudiomagazine.com/articles/2009/02/01/use-iterators-in-vb-now.aspx

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The new Async CTP includes support for Yield in VB.NET.

See Iterators in Visual Basic for information on usage.

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See my answers here:

• Yield in VB.NET
• Iterator pattern in VB.NET (C# would use yield!)

To summarize:
VB.Net does not have yield, but C# implements yield by converting your code to a state machine behind that scenes. VB.Net's Static keyword also allows you to store state within a function, so in theory you should be able to implement a class that allows you to write similar code when used as a Static member of a method.

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No yield return in VB.NET :( Just create a list and return it.

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Behind the scenes, the compiler creates an enumerator class to do the work. Since VB.NET does not implement this pattern, you have to create your own implementation of IEnumerator(Of T)

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Below gives output: 2, 4, 8, 16, 32

In VB,

Public Shared Function setofNumbers() As Integer()

    Dim counter As Integer = 0
    Dim results As New List(Of Integer)
    Dim result As Integer = 1
    While counter < 5
        result = result * 2
        results.Add(result)
        counter += 1
    End While
    Return results.ToArray()
End Function

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    For Each i As Integer In setofNumbers()
        MessageBox.Show(i)
    Next
End Sub

In C#

   private void Form1_Load(object sender, EventArgs e)
    {
        foreach (int i in setofNumbers())
        {
            MessageBox.Show(i.ToString());
        }
    }

    public static IEnumerable<int> setofNumbers()
    {
        int counter=0;
        //List<int> results = new List<int>();
        int result=1;
        while (counter < 5)
        {
          result = result * 2;
          counter += 1;
          yield return result;
        }
    }