Enumerable.Where 可以对任何可枚举的事物进行任意过滤，它是在 委托 的帮助下完成的，这是 VBA 不知道或无法实现的。
警告以下是不适合生产使用的实验代码。它按原样提供用于教育目的。使用风险自负。
你可以 模拟它。请参阅代码审查中的 Wait, is this... LINQ? 和 Generating and calling code on the fly - 下面是我称为 Delegate 的类 - 请注意，它的 PredeclaredId 属性设置为 True，因此可以调用其 Create 工厂方法默认实例。它使用正则表达式库来解析函数的定义，并使用 VBE 可扩展性 API 库在给定字符串的情况下生成一个“匿名函数”，例如：
Set x = Delegate.Create("(x) => MsgBox(""Hello, "" & x & ""!"")")
x.Execute "Mug"
上面的代码生成并调用了这个函数：
Public Function AnonymousFunction(ByVal x As Variant) As Variant
AnonymousFunction = MsgBox("Hello, " & x & "!")
End Function
这会产生你所期望的：
委托类
Option Explicit
Private Type TDelegate
Body As String
Parameters As New Collection
End Type
Private Const methodName As String = "AnonymousFunction"
Private this As TDelegate
Friend Property Get Body() As String
Body = this.Body
End Property
Friend Property Let Body(ByVal value As String)
this.Body = value
End Property
Public Function Create(ByVal expression As String) As Delegate
Dim result As New Delegate
Dim regex As New RegExp
regex.Pattern = "\((.*)\)\s\=\>\s(.*)"
Dim regexMatches As MatchCollection
Set regexMatches = regex.Execute(expression)
If regexMatches.Count = 0 Then
Err.Raise 5, "Delegate", "Invalid anonymous function expression."
End If
Dim regexMatch As Match
For Each regexMatch In regexMatches
If regexMatch.SubMatches(0) = vbNullString Then
result.Body = methodName & " = " & Right(expression, Len(expression) - 6)
Else
Dim params() As String
params = Split(regexMatch.SubMatches(0), ",")
Dim i As Integer
For i = LBound(params) To UBound(params)
result.AddParameter Trim(params(i))
Next
result.Body = methodName & " = " & regexMatch.SubMatches(1)
End If
Next
Set Create = result
End Function
Public Function Execute(ParamArray params()) As Variant
On Error GoTo CleanFail
Dim paramCount As Integer
paramCount = UBound(params) + 1
GenerateAnonymousMethod
'cannot break beyond this point
Select Case paramCount
Case 0
Execute = Application.Run(methodName)
Case 1
Execute = Application.Run(methodName, params(0))
Case 2
Execute = Application.Run(methodName, params(0), params(1))
Case 3
Execute = Application.Run(methodName, params(0), params(1), params(2))
Case 4
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3))
Case 5
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4))
Case 6
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4), params(5))
Case 7
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4), params(5), _
params(6))
Case 8
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4), params(5), _
params(6), params(7))
Case 9
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4), params(5), _
params(6), params(7), params(8))
Case 10
Execute = Application.Run(methodName, params(0), params(1), params(2), _
params(3), params(4), params(5), _
params(6), params(7), params(8), _
params(9))
Case Else
Err.Raise 5, "Execute", "Too many parameters."
End Select
CleanExit:
DestroyAnonymousMethod
Exit Function
CleanFail:
Resume CleanExit
End Function
Friend Sub AddParameter(ByVal paramName As String)
this.Parameters.Add "ByVal " & paramName & " As Variant"
End Sub
Private Sub GenerateAnonymousMethod()
Dim component As VBComponent
Set component = Application.VBE.VBProjects("Reflection").VBComponents("AnonymousCode")
Dim params As String
If this.Parameters.Count > 0 Then
params = Join(Enumerable.FromCollection(this.Parameters).ToArray, ", ")
End If
Dim signature As String
signature = "Public Function " & methodName & "(" & params & ") As Variant" & vbNewLine
Dim content As String
content = vbNewLine & signature & this.Body & vbNewLine & "End Function" & vbNewLine
component.CodeModule.DeleteLines 1, component.CodeModule.CountOfLines
component.CodeModule.AddFromString content
End Sub
Private Sub DestroyAnonymousMethod()
Dim component As VBComponent
Set component = Application.VBE.VBProjects("Reflection").VBComponents("AnonymousCode")
component.CodeModule.DeleteLines 1, component.CodeModule.CountOfLines
End Sub
您需要将VBProjects("Reflection").VBComponents("AnonymousCode") 更改为指向您的VBA 项目中的某个空标准模块...或者为Execute 方法创建一个名为Reflection 的项目和一个名为AnonymousCode 的空标准模块将函数生成到。
作为 VBA 代码如何编译的工件，生成的代码可以执行，但您不能在其中放置断点，并且 VBE 将拒绝在生成的代码内部中断 - 所以无论您提供工厂的任何字符串方法，您最好确保它足够简单，可以 100% 无错误。
这给你的是一个封装特定动作的对象：这个对象可以作为参数传递，就像任何其他对象一样 - 所以如果你有自己的集合类实现（这里LinqEnumerable)，那么你可以用它来实现一个Where方法，它接受一个Delegate参数，假设predicate参数封装了一个返回Boolean的函数：
Public Function Where(ByVal predicate As Delegate) As LinqEnumerable
Dim result As LinqEnumerable
Set result = New LinqEnumerable
Dim element As Variant
For Each element In encapsulated
If predicate.Execute(element) Then result.Add element
Next
Set Where = result
End Function
因此，给定自定义集合类，您可以创建一个定义自定义条件的Delegate 实例，将其传递给Where 方法，然后返回过滤结果。
您甚至可以进一步推动它并实现Aggregate 方法：
Public Function Aggregate(ByVal accumulator As Delegate) As Variant
Dim result As Variant
Dim isFirst As Boolean
Dim value As Variant
For Each value In encapsulated
If isFirst Then
result = value
isFirst = False
Else
result = accumulator.Execute(result, value)
End If
Next
Aggregate = result
End Function
并像使用 C# LINQ 一样运行它，减去编译时类型安全和延迟执行：
Dim accumulator As Delegate
Set accumulator = Delegate.Create("(work,value) => value & "" "" & work")
Debug.Print LinqEnumerable.FromList(List.Create("the", "quick", "brown", "fox")) _
.Aggregate(accumulator)
输出：
fox brown quick the
这项工作是 GitHub 上 VBEX 存储库中 Lambda 内容的基础（最初由 Rubberduck 项目的联合创始人 Chris McClellan 提供；不过大部分工作可以归功于 Philip Wales）- 100%-VBA 项目，为您提供其他几个类可供使用。我鼓励您探索这些，看看是否有更适合生产使用。