如何判断一个对象是否支持标量比较？

Question

有没有人能快速了解一下我将如何检查给定类是否支持 >、= 和 运营商？

给定一个传入的对象，我正在寻找实现以下逻辑的代码：

If GetType(someObj).SupportsScalarComparisons() Then ... 

我不知道这是反射的情况，还是？提前致谢。

Answer 1

我认为这是一个有趣的问题，所以我决定使用反射来提出解决方案。 （不知道除了反射还有没有其他办法。）

---

Imports System.Reflection

Module MainModule

    Sub Main()

        'primitive, value type
        If GetType(Integer).SupportsScalarComparisons Then
            Debug.WriteLine("Integer supports comparisions")
        Else
            Debug.WriteLine("Integer does not support comparisions")
        End If

        'non-primitive, value type
        If GetType(Decimal).SupportsScalarComparisons Then
            Debug.WriteLine("Decimal supports comparisions")
        Else
            Debug.WriteLine("Decimal does not support comparisions")
        End If

        'non-primitive, object type
        If GetType(Version).SupportsScalarComparisons Then
            Debug.WriteLine("Version supports comparisions")
        Else
            Debug.WriteLine("Version does not support comparisions")
        End If

        'non-primitive, object type
        If GetType(String).SupportsScalarComparisons Then
            Debug.WriteLine("String supports comparisions")
        Else
            Debug.WriteLine("String does not support comparisions")
        End If

        'Integer supports comparisions
        'Decimal supports comparisions
        'Version supports comparisions
        'String does not support comparisions

    End Sub

    Public Sub Dump(ByVal type As Type)
        Dim oMethod() As MethodInfo = type.GetMethods(BindingFlags.Static Or BindingFlags.Public)
        For Each o As MethodInfo In oMethod
            Debug.WriteLine(o.Name)
        Next
    End Sub

End Module

Public Module TypeExtensions

    <System.Runtime.CompilerServices.Extension()> _
    Public Function SupportsScalarComparisons(ByVal obj As Type) As Boolean
        Static Methods() As String = {"op_GreaterThan", "op_Equality", "op_LessThan"}

        If obj.IsPrimitive Then
            Return True
        End If

        For Each sMethodName As String In Methods
            Dim oMethod As MethodInfo = obj.GetMethod(sMethodName, BindingFlags.Public Or BindingFlags.Static)
            If oMethod Is Nothing Then
                'does not support
                Return False
            End If
        Next

        Return True

        'List is from MSDN Library index
        'op_Addition
        'op_BitwiseAnd
        'op_BitwiseOr
        'op_Decrement
        'op_Division
        'op_Equality
        'op_ExculsiveOr
        'op_Explicit
        'op_False
        'op_GreaterThan
        'op_GreaterThanOrEqual
        'op_Implicit
        'op_Increment
        'op_Inequality
        'op_LogicalNot
        'op_LessThan
        'op_LessThanOrEqual
        'op_Modulus
        'op_Multiply
        'op_OnesComplement
        'op_Subtraction
        'op_True
        'op_UnaryNegation
        'op_UnaryPlus

    End Function

End Module

Answer 2

尝试 Catch 任何你想做的事情......如果你 CATCH 那么你就做不到。