从 C# 转换为 VB.NET 产量 [重复]

Question

我知道 VB.NET 没有 yield 关键字，那么你将如何转换枚举的 yield。在下面的代码中？

    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;
    }

编辑：这适用于 .NET 2.0

有什么想法吗？

谢谢，

Answer 1

当前版本的 VB.Net 确实支持 yield 关键字。我使用了自动转换from here 来生成这段代码。

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

如果您不能使用 yield，您需要一个列表来存储结果，然后在循环结束时返回它。例如：

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

Answer 2

解决方案在这个问题中：Yield in VB.NET。

如上所述，这个关键字现在是 VB 的一部分，如果您使用的是旧版本的 VB.Net，请查看链接。

Answer 3

我在网上找到的例子是

C#代码

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);
    }
}
}

/* 输出： 2 4 8 16 32 64 128 256 */

与 Visual C# 示例给出相同结果的 VB.Net 代码。

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

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