TypeName
|
DoNotDeclareStaticMembersOnGenericTypes
|
CheckId
|
CA1000
|
Category
|
Microsoft.Design
|
Breaking Change
|
Breaking
|
An externally visible generic type contains a static (Shared in Visual Basic) member.
When a static member of a generic type is called, the type argument must be specified for the type. When a generic instance member that does not support inference is called, the type argument must be specified for the member. The syntax for specifying the type argument in these two cases is different and easily confused, as the following calls demonstrate:
' Shared method in a generic type.
GenericType(Of Integer).SharedMethod()
' Generic instance method that does not support inference.
someObject.GenericMethod(Of Integer)()
// Static method in a generic type.
GenericType<int>.StaticMethod();
// Generic instance method that does not support inference.
someObject.GenericMethod<int>();
Generally, both of the prior declarations should be avoided so that the type argument does not have to be specified when the member is called. This results in a syntax for calling members in generics that is no different from the syntax for non-generics. For more information, see Generic methods should provide type parameter.
To fix a violation of this rule, remove the static member or change it to an instance member.
When to Suppress Warnings
Do not suppress a warning from this rule. Providing generics in a syntax that is easy to understand and use reduces the time that is required to learn and increases the adoption rate of new libraries.
The following example shows a method that causes this violation.
Imports System
Imports System.Runtime.InteropServices
Namespace Samples
Public NotInheritable Class EnumParser(Of T)
Private Sub New()
End Sub
' Fires this violation
Public Shared Function TryParse(ByVal value As String, <Out()> ByRef result As T) As Boolean
Try
result = DirectCast([Enum].Parse(GetType(T), value), T)
Return True
Catch ex As ArgumentException
End Try
result = Nothing
Return False
End Function
End Class
Module Program
Public Sub Main()
Dim result As DayOfWeek
' Must specify type argument
If EnumParser(Of DayOfWeek).TryParse("Monday", result) Then
Console.WriteLine("Conversion Succeeded!")
End If
End Sub
End Module
End Namespace
using System;
namespace Samples
{
public static class EnumParser<T>
{ // Fires this violation
public static bool TryParse(string value, out T result)
{
try
{
result = (T)Enum.Parse(typeof(T), value);
return true;
}
catch (ArgumentException)
{
}
result = default(T);
return false;
}
}
static class Program
{
public static void Main()
{
DayOfWeek dayOfWeek;
// Must specify type argument
if (EnumParser<DayOfWeek>.TryParse("Monday", out dayOfWeek))
{
Console.WriteLine("Conversion Succeeded!");
}
}
}
}
In the example above, declaring a static member on a generic type forces the user to specify the type argument when calling it.
The following example fixes the above violation by moving the type parameter, T, from the class to the method, allowing it to be inferred by the compiler when called.
Avoid excessive parameters on generic types
Collections should implement generic interface
Do not expose generic lists
Do not nest generic types in member signatures
Generic methods should provide type parameter
Use generic event handler instances
Use generics where appropriate
Reference