abstract_sealed_class

A 'sealed' class can't be marked 'abstract' because it's already implicitly abstract.

The analyzer produces this diagnostic when a class is declared using both the modifier abstract and the modifier sealed. Sealed classes are implicitly abstract, so explicitly using both modifiers is not allowed.

The following code produces this diagnostic because the class C is declared using both abstract and sealed:

abstract sealed class C {}

If the class should be abstract but not sealed, then remove the sealed modifier:

abstract class C {}

If the class should be both abstract and sealed, then remove the abstract modifier:

sealed class C {}