为什么允许在密封类中编写受保护的成员？

Question

密封类是一个不能继承的类，为什么允许在密封类中编写受保护的成员

Answer 1

Because Microsoft decided it to not be an error.

I agree that it makes no sense to declare a protected member in a sealed class. Using protected on a member in a sealed class is the same as having a private member

Therefore you will get the following compiler warning: https://docs.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2008/7x8ekes3(v=vs.90)

Answer 2

Sealed classes can still have inherited Protected members, so to me it makes sense. Maybe the designers did this to allow inheritance without needing to make a special compiler case.

public class Foo
{
    protected virtual string Name { get; set; } = "Foo";
}

public sealed class Bar : Foo
{
    protected override string Name { get; set; } = "Bar";
}

Update: From Eric Lippert in 2009 :

The language design notes document that the decision to make introducing a virtual method into a sealed type an error was made on the 18th of October, 1999, but does not give any justification for the decision. I can find nowhere in the notes that justifies why introducing a new protected member ought to be legal. My best guess: this was probably simply an oversight in the first version, and then it became a breaking change to ever fix it. – Eric Lippert