Question

是否可以将通用T2限制为而不是为T1或其任何子类？

我有以下两种方法重载：

Sub Foo(Of T1, T2)(arg1 As T1, arg2 As T2) ' 1
Sub Foo(Of T)(arg1 As T, arg2 As T)        ' 2

我可以以任何方式定义这些方法，以便这些代码行解析为

Foo(1, True) ' 1
Foo(1, 1)    ' 2

目前，除非我明确写

，否则第二次调用是不明确的

Foo(1, True)
Foo(Of Integer)(1, 1)

类型约束(Of T1, T2 As T1)允许我将T2限制为T1及其子类。但是我可以编写任何内容来实现相反的目的，这样第一次重载只会匹配T2 不是 T1（或者它的任何子类，但是那个＆＃39; s甚至与我无关）？

我可以保证，在我的情况下T1和T2永远不会在任何方向上继承或转换。它们是大约一千个类的池中的任意两个，这就是为什么我不能创建所有类型的非泛型交叉产品的原因。

Answer 1

您需要的东西似乎不可能，因为任何限制都是针对单个参数而不是组合。有一个解决方案在运行时而不是在编译时决定。

您想要：

Sub Foo(Of T1, T2)(arg1 As T1, arg2 As T2) 
   Do1()
End Sub

Sub Foo(Of T)(arg1 As T, arg2 As T)        
   Do2()
End Sub

您可以：

Sub Foo(Of T1, T2)(arg1 As T1, arg2 As T2) 
    If arg1.GetType() is arg2.GetType() Then
       Do2()
    else
       Do1()
    End If          
End Sub

这不是很好，但有点慢，但解决了问题。

Answer 2

就我而言，我的目标是通过使用两个泛型标记Obsolete来禁止使用两个不同类型的参数。我实际上通过使用扩展程序找到了一种方法：

Public Class Bar

  Public Sub Foo(Of T)(arg1 As T, arg2 As T)
    DoStuff()
  End Sub

End Class

Public Module BarExtensions

  <Obsolete("A good explanation of what's wrong", True)>
  <Extension>
  Public Sub Foo(Of T1, T2)(bar As Bar, arg1 As T1, arg2 As T2)
    ' I could make this work, but any code calling this is most likely wrong
    Throw New ArgumentException()
  End Sub

End Module

这允许我警告用户他们的代码有些可疑：

Public Class Baz

  Public Sub WrongCodeDoingDangerousThings(bar As Bar)
    Dim x1 As Double = 1d
    Dim x2 As Double = 2d
    Dim x3 As Integer = 3

    bar.Foo(x1, x2) ' OK, no resolve conflict
    bar.Foo(x1, x3) ' Won't compile with "A good explanation of what's wrong"

    ' This works because conflicts between an extension and an instance
    ' method are automatically resolved in favor of the instance method
  End Sub

End Class

将泛型类型参数限制为不是VB.NET中的另一个泛型类型参数

2 个答案: