CA1007: Use generics where appropriate


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The latest version of this topic can be found at CA1007: Use generics where appropriate.

|Breaking Change|Breaking|

An externally visible method contains a reference parameter of type System.Object, and the containing assembly targets .NET Framework 2.0.

A reference parameter is a parameter that is modified by using the ref (ByRef in Visual Basic) keyword. The argument type that is supplied for a reference parameter must exactly match the reference parameter type. To use a type that is derived from the reference parameter type, the type must first be cast and assigned to a variable of the reference parameter type. Use of a generic method allows all types, subject to constraints, to be passed to the method without first casting the type to the reference parameter type.

To fix a violation of this rule, make the method generic and replace the Object parameter by using a type parameter.

Do not suppress a warning from this rule.

The following example shows a general-purpose swap routine that is implemented as both nongeneric and generic methods. Note how efficiently the strings are swapped by using the generic method compared to the nongeneric method.

Imports System

Namespace DesignLibrary

   Public NotInheritable Class ReferenceParameters
      Private Sub New()
      End Sub

      ' This method violates the rule.
      Public Shared Sub Swap( _  
         ByRef object1 As Object, ByRef object2 As Object)

         Dim temp As Object = object1
         object1 = object2
         object2 = temp

      End Sub

      ' This method satifies the rule.
      Public Shared Sub GenericSwap(Of T)( _ 
         ByRef reference1 As T, ByRef reference2 As T)
         Dim temp As T = reference1
         reference1 = reference2
         reference2 = temp

      End Sub

   End Class

   Class Test
      Shared Sub Main()
         Dim string1 As String = "Swap"
         Dim string2 As String = "It"

         Dim object1 As Object = DirectCast(string1, Object)
         Dim object2 As Object = DirectCast(string2, Object)
         ReferenceParameters.Swap(object1, object2)
         string1 = DirectCast(object1, String)
         string2 = DirectCast(object2, String)
         Console.WriteLine("{0} {1}", string1, string2)

         ReferenceParameters.GenericSwap(string1, string2)
         Console.WriteLine("{0} {1}", string1, string2)

      End Sub

   End Class

End Namespace

CA1005: Avoid excessive parameters on generic types

CA1010: Collections should implement generic interface

CA1000: Do not declare static members on generic types

CA1002: Do not expose generic lists

CA1006: Do not nest generic types in member signatures

CA1004: Generic methods should provide type parameter

CA1003: Use generic event handler instances