VB.NET中的迭代器模式（C#会使用产量！）。[英] Iterator pattern in VB.NET (C# would use yield!)

问题描述

How do implement the iterator pattern in VB.NET, which does not have the yield keyword?

推荐答案

This is now supported in VS 2010 SP1, with the Async CTP, see: Iterators (C# and Visual Basic) on MSDN and download Visual Studio Async CTP (Version 3).

Code such as this, works:

Private Iterator Function SomeNumbers() As IEnumerable
    ' Use multiple yield statements.
    Yield 3
    Yield 5
    Yield 8
End Function

其他推荐答案

VB.NET does not support the creation of custom iterators and thus has no equivalent to the C# yield keyword. However, you might want to look at the KB article How to make a Visual Basic .NET or Visual Basic 2005 class usable in a For Each statement for more information.

其他推荐答案

Hmm, looks like you might be out of luck:

I was struggling with an issue today when converting some C# to VB.NET. C# has a really cool "yield return" statement that is used in an iterator block to provide a value to the enumerator object. VB.NET does not have the "yield" keyword. So, there are a few solutions (none of which are really clean) to get around this. You could use a return statement to return the value if you are looping through and would like to break an enumerator and return a single value. However, if you'd like to return the entire enumeration, create a List() of the child type and return the list. Since you are usually using this with an IEnumerable, the List() will work nice.

That was written a year ago, not sure if anyone has come up with anything else better since then..

Edit: this will be possible in the version 11 of VB.NET (the one after VS2010), support for iterators is planned. The spec is available here.