The C# Scopes for Privileged Inheritance
You can't really combine the various scopes that you can apply to a C# member because, I suspect, they wouldn't make sense (what's the scope of a public private method, for example?). However, you can combine internal with private and protected like this:
public class CustomerBase
{
protected internal void DeleteCustomer() {
or
public class CustomerBase
{
private protected void DeleteCustomer() {
In my first example, because of its internal scope, DeleteCustomer can be used by code that instantiates CustomerBase but only if that code is in the same project as CustomerBase. Because of the protected declaration, however, code in other projects can access DeleteCustomer through a class that inherits from CustomerBase.
Code in other projects that instantiate CustomerBase directly won't see DeleteCustomer. Essentially, code in the same project as CustomerBase has a privilege denied to code in other projects (the ability to delete customers, in this case).
The scope private protected goes even further and is probably more useful. This scope prevents DeleteCustomer from being accessed except through classes that derive from CustomerBase and only if those derived classes are in the same project as CustomerBase.
Code in some other project in a class that inherits from CustomerBase won't be able to access DeleteCustomer. This allows you to create derived classes in the same project as CustomerBase that have privileges denied to classes in other projects that inherit from CustomerBase.
Posted by Peter Vogel on 02/21/2018