CA1048: Do not declare virtual members in sealed types

Note

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Item	Value
TypeName	DoNotDeclareVirtualMembersInSealedTypes
CheckId	CA1048
Category	Microsoft.Design
Breaking Change	Breaking

Cause

A public type is sealed and declares a method that is both virtual (Overridable in Visual Basic) and not final. This rule does not report violations for delegate types, which must follow this pattern.

Rule Description

Types declare methods as virtual so that inheriting types can override the implementation of the virtual method. By definition, you cannot inherit from a sealed type, making a virtual method on a sealed type meaningless.

The Visual Basic .NET and C# compilers do not allow types to violate this rule.

How to Fix Violations

To fix a violation of this rule, make the method non-virtual or make the type inheritable.

When to Suppress Warnings

Do not suppress a warning from this rule. Leaving the type in its current state can cause maintenance issues and does not provide any benefits.

Example

The following example shows a type that violates this rule.

using namespace System;

namespace DesignLibrary
{                        
    public ref class SomeType sealed
    {
    public:
        virtual bool VirtualFunction() { return true; }
    };
}