Converting to VB.NET from C# yield

Question

I understand VB.NET does not have yield keyword so how would you convert yield of enum. in the following code?

    private static IEnumerable<int> Combinations(int start, int level, int[] arr)
    {
        for (int i = start; i < arr.Length; i++)
            if (level == 1)
                yield return arr[i];
            else
                foreach (int combination in Combinations(i + 1, level - 1, arr))
                    yield return arr[i] * combination;
    }

Edit: This is for .NET 2.0

Any idea?

Thanks,

I don't do VB, but you'll need to create a list to push the results into then return that. — Dave Hillier, Aug 06 '13 at 10:28
Which version of VB are you using? VB 11 has iterator blocks... See http://msdn.microsoft.com/en-us/library/hh156729.aspx — Jon Skeet, Aug 06 '13 at 10:29
The solution is in this question: [http://stackoverflow.com/questions/97381/yield-in-vb-net](http://stackoverflow.com/questions/97381/yield-in-vb-net) — glautrou, Aug 06 '13 at 12:00

Dave Hillier · Accepted Answer · 2013-08-06T10:35:27.903

Current versions of VB.Net do support the yield keyword. I used an automatic conversion from here to generate this code.

Private Shared Function Combinations(start As Integer, level As Integer, arr As Integer()) As IEnumerable(Of Integer)
    For i As Integer = start To arr.Length - 1
        If level = 1 Then
            yield Return arr(i)
        Else
            For Each combination As Integer In Combinations(i + 1, level - 1, arr)
                yield Return arr(i) * combination
            Next
        End If
    Next
End Function

If you can't use yield you need a list to store the results, and then return that at the end of the loop. For example:

Private Shared Function Combinations(start As Integer, level As Integer, arr As Integer()) As IEnumerable(Of Integer)
    Dim result As New List(Of Integer)()
    For i As Integer = start To arr.Length - 1
        If level = 1 Then
            result.Add(arr(i))
        Else
            For Each combination As Integer In Combinations(i + 1, level - 1, arr)
                result.Add(arr(i) * combination)
            Next
        End If
    Next
    Return result
End Function

Sorry this is for VB.NET 2.0 which does not support Yield keyword so it does not work. — activebiz, Aug 06 '13 at 10:32
Clearly not the version you're using but it does work: http://msdn.microsoft.com/en-us/library/hh156729.aspx although I've added a variant to show how you'd do it without yield — Dave Hillier, Aug 06 '13 at 10:33
As always with automatic converted code, the result is wrong (the converter is clearly out-dated and does not support VB.Net's iterator blocks). First of all, the function has to be marked with the `Iterator` keyword: `Private Shared Iterator Function Combinations`. Also, it's just `yield `, not `yield return `. — sloth, Apr 07 '14 at 08:04

score 0 · Answer 2 · edited May 23 '17 at 12:29

0

The solution is in this question: Yield in VB.NET.

As said above this keyword is now part of VB, look at the link if you are using an old version of VB.Net.

edited May 23 '17 at 12:29

Community

1
1

answered Aug 06 '13 at 12:03

glautrou

3,140
2
29
34

score -1 · Answer 3 · answered Aug 06 '13 at 10:34

The example that i found on internet was

C# CODE

public class List
{
//using System.Collections; 
public static IEnumerable Power(int number, int exponent)
{
    int counter = 0;
    int result = 1;
    while (counter++ < exponent)
    {
        result = result * number;
        yield return result;
    }
}

static void Main()
{
    // Display powers of 2 up to the exponent 8: 
    foreach (int i in Power(2, 8))
    {
        Console.Write("{0} ", i);
    }
}
}

/* Output: 2 4 8 16 32 64 128 256 */

VB.Net code that gives the same result as the Visual C# example.

Option Strict On
Option Explicit On
Option Infer Off

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

    Dim results As System.Collections.Generic.IEnumerable(Of Integer)
    results = Power(2, 8)

    Dim sb As New System.Text.StringBuilder
    For Each num As Integer In results
        sb.Append(num.ToString & " ")
    Next

    MessageBox.Show(sb.ToString)

End Sub

Public Function Power(ByVal number As Integer, ByVal exponent As Integer) As System.Collections.Generic.IEnumerable(Of Integer)

    Dim result As New List(Of Integer)

    For index As Integer = 1 To exponent
        result.Add(Convert.ToInt32(Math.Pow(number, index)))
    Next
    Return result.AsEnumerable

End Function

End Class

References --> http://msdn.microsoft.com/en-us/library/9k7k7cf0(v=vs.90).aspx

Seems as if you didnt read the reference web page. It is clearly mentioned there. And your confusion should be cleared. — Nisarg Shah, Aug 06 '13 at 10:38

Converting to VB.NET from C# yield

3 Answers3