在 vb.net 中从 lambda 调用子例程

Question

我发现自己经常从 lambda 调用函数，因为提供的委托不匹配或没有足够的参数。令人恼火的是我不能在子例程上执行 lambda 操作。每次我想这样做时，我都必须将子例程包装在一个不返回任何内容的函数中。不漂亮，但它有效。

有没有另一种方法可以使这个过程更平滑/更漂亮？

我读到，整个 lambda 不足可能会在 VS2010/VB10 中得到修复，所以我的问题更多是出于好奇。

一个简单的例子：

Public Class ProcessingClass
    Public Delegate Sub ProcessData(ByVal index As Integer)
    Public Function ProcessList(ByVal processData As ProcessData)
        ' for each in some list processData(index) or whatever'
    End Function
End Class

Public Class Main

    Private Sub ProcessingSub(ByVal index As Integer, _
                              ByRef result As Integer)
        ' (...) My custom processing '
    End Sub

    Private Function ProcessingFunction(ByVal index As Integer, _
                                        ByRef result As Integer) As Object
        ProcessingSub(index, result)
        Return Nothing
    End Function

    Public Sub Main()
        Dim processingClass As New ProcessingClass
        Dim result As Integer
        ' The following throws a compiler error as '
        ' ProcessingSub does not produce a value'
        processingClass.ProcessList( _
            Function(index As Integer) ProcessingSub(index, result))
        ' The following is the workaround that'
        ' I find myself using too frequently.'
        processingClass.ProcessList( _
            Function(index As Integer) ProcessingFunction(index, result))
    End Sub

End Class

Answer 1

如果您发现您经常使用相同类型的数据，那么您可以将委托包装在一个类中。

创建一个转换为委托的基类：

Public MustInherit Class ProcessDataBase
    Public Shared Widening Operator CType(operand As ProcessDataBase) as ProcessingClass.ProcessData
        Return AddressOf operand.Process
    End Sub

    Protected MustOverride Sub Process(index As Integer)  
End Class

从该类继承：

Public Class ProcessResult
    Inherits ProcessDataBase

    Public Result As Integer

    Protected Overrides Sub Process(index as Integer)
        ' Your processing, result is modified.
    End SUb
End Class

使用它：

Public Class Main()
    Public Sub Main()
        Dim processingClass As New ProcessingClass
        Dim processor As New ProcessResult

        processingClass.ProcessList(processor)
        Dim result as integer=processor.Result
    End Sub
End Class

Answer 2

它已在 VB10 中修复，VS10 Beta 已可用（如果有）一个供您使用的选项。在 VB10 中，您有没有返回值的 lambda 表达式和内联子函数/函数。

现在，也许您可​​以忘记 lambda 并使用委托来代替？像这样的东西：

processingClass.ProcessList(AddressOf ProcessingSub)