Compiler Error CS0549
'function' is a new virtual member in sealed class 'class'
A sealedclass cannot be used as a base class. Therefore, it is useless to have a virtual method in sealed class.
The following sample generates CS0549:
// CS0549.cs
// compile with: /target:library
sealed public class MyClass
{
virtual public void TestMethod() {} // CS0549
public void TestMethod2() {} // OK
}