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在dotnet中为具有任意数量参数的函数使用泛型?

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Zarigani · 技术社区 · 15 年前

我想要一个可以“包装”任何其他函数调用的函数。在这种特殊情况下,它允许我围绕某些特定操作编写一些更通用的事务处理。

我可以为任何特定数量的参数编写此文件,例如,对于一个参数:

Public Shared Sub WrapFunc(Of T)(ByVal f As Action(Of T), ByVal arg As T)
    ' Test some stuff, start transaction
    f(arg)
    ' Test some stuff, end transaction
End Sub

…但我希望这个句柄可以处理任意数量的参数,而不必对0个参数、1个参数、2个参数等有重复的代码。

有办法吗?

[编辑]感谢罗伯特·弗雷泽的C代码。以下是对vb的翻译:

[Edit2]已更正代码。不幸的是,在vb中似乎没有办法使用单独的“actasfunc”函数。从好的方面来说,这些闭包对任何使用闭包的人都是隐藏的,并且闭包是可重用的。

Public Shared Sub WrapFunc(ByVal f As Action)
    _WrapFunc(f)
End Sub
Public Shared Sub WrapFunc(Of T1)(ByVal f As Action(Of T1), ByVal arg1 As T1)
    _WrapFunc(Closure(f, arg1))
End Sub
Public Shared Sub WrapFunc(Of T1, T2)(ByVal f As Action(Of T1, T2), ByVal arg1 As T1, ByVal arg2 As T2)
    _WrapFunc(Closure(f, arg1, arg2))
End Sub

Private Shared Sub _WrapFunc(ByVal f As Action)
    ' Test some stuff, start transaction
    f()
    ' Test some stuff, end transaction
End Sub

Private Shared Function Closure(Of T1)(ByVal f As Action(Of T1), ByVal arg1 As T1) As Action
    Return New Action(Function() _ActAsFunc(f, arg1))
End Function
Private Shared Function Closure(Of T1, T2)(ByVal f As Action(Of T1, T2), ByVal arg1 As T1, ByVal arg2 As T2) As Action
    Return New Action(Function() _ActAsFunc(f, arg1, arg2))
End Function

Private Shared Function _ActAsFunc(Of T1)(ByVal f As Action(Of T1), ByVal arg1 As T1) As Object
    f(arg1) : Return Nothing
End Function
Private Shared Function _ActAsFunc(Of T1, T2)(ByVal f As Action(Of T1, T2), ByVal arg1 As T1, ByVal arg2 As T2) As Object
    f(arg1, arg2) : Return Nothing
End Function

3 回复 | 直到 15 年前

Robert Fraser 15 年前

不。我也希望有,我一直这样做。

在内部,ms使用文本模板/代码生成工具生成重复代码。C中的一个选项是围绕参数创建闭包,然后将它们作为无参数System.Action传递给另一个函数;我不确定VB.NET是否支持这一点。

下面是我在c中所做的,希望有vb.net经验的人能翻译一下:

public void add(Action action, EventFlags flags) { addInternal(action, flags); }
public void add<T1>(Action<T1> action, T1 p1, EventFlags flags) { addInternal(closure(action, p1), flags); }
public void add<T1, T2>(Action<T1, T2> action, T1 p1, T2 p2, EventFlags flags) { addInternal(closure(action, p1, p2), flags); }
public void add<T1, T2, T3>(Action<T1, T2, T3> action, T1 p1, T2 p2, T3 p3, EventFlags flags) { addInternal(closure(action, p1, p2, p3), flags); }
public void add<T1, T2, T3, T4>(Action<T1, T2, T3, T4> action, T1 p1, T2 p2, T3 p3, T4 p4, EventFlags flags) { addInternal(closure(action, p1, p2, p3, p4), flags); }

private static Action closure<T1>(Action<T1> action, T1 p1) { return () => action(p1); }
private static Action closure<T1, T2>(Action<T1, T2> action, T1 p1, T2 p2) { return () => action(p1, p2); }
private static Action closure<T1, T2, T3>(Action<T1, T2, T3> action, T1 p1, T2 p2, T3 p3) { return () => action(p1, p2, p3); }
private static Action closure<T1, T2, T3, T4>(Action<T1, T2, T3, T4> action, T1 p1, T2 p2, T3 p3, T4 p4) { return () => action(p1, p2, p3, p4); }

Benjamin Anderson 15 年前

你不能用paramarray吗?

  Public Shared Sub WrapFunc(Of T)(ByVal f As Action(Of T), ByVal ParamArray args() As T)
        ' Test some stuff, start transaction
        For Each arg As T In args
            f(arg)
        Next

        ' Test some stuff, end transaction
    End Sub

Steve Wortham 15 年前

我没试过用泛型,但是 ParamArray ?

Public Shared Sub WrapFunc(Of T)(ByVal f As Action(Of T()), ByVal ParamArray args() As T)
    ' Test some stuff, start transaction
    f(args)
    ' Test some stuff, end transaction
End Sub