Use generics where appropriate

Cause

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

Rule Description

A reference parameter is a parameter modified with the ref (ByRef in Visual Basic) keyword. The argument type supplied for a reference parameter must exactly match the reference parameter type. To use a type 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.

How to Fix Violations

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

When to Exclude Warnings

Do not exclude a warning from this rule.

Example

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

using System;

namespace DesignLibrary
{
   public sealed class ReferenceParameters
   {
      private ReferenceParameters(){}

      // This method violates the rule.
      public static void Swap(ref object object1, ref object object2)
      {
         object temp = object1;
         object1 = object2;
         object2 = temp;
      }

      // This method satifies the rule.
      public static void GenericSwap<T>(ref T reference1, ref T reference2)
      {
         T temp = reference1;
         reference1 = reference2;
         reference2 = temp;
      }
   }

   class Test
   {
      static void Main()
      {
         string string1 = "Swap";
         string string2 = "It";

         object object1 = (object)string1;
         object object2 = (object)string2;
         ReferenceParameters.Swap(ref object1, ref object2);
         string1 = (string)object1;
         string2 = (string)object2;
         Console.WriteLine("{0} {1}", string1, string2);

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

Related Rules

Avoid excessive parameters on generic types

Collections should implement generic interface

Do not declare static members on generic types

Do not expose generic lists

Do not nest generic types in member signatures

Generic methods should provide type parameter

Use generic event handler instances

See Also

Concepts

Generics (C# Programming Guide)