Why is DefaultSentenceBuilder private?

[asherber]

Is there a reason that DefaultSentenceBuilder is marked private? It would be much easier to customize SentenceBuilder if the class were public and could be inherited.

public class MySentenceBuilder: DefaultSentenceBuilder
{
   public override Func<string> UsageHeadingText => () => "Usage:";
}

SentenceBuilder.Factory = () => new MySentenceBuilder();

Another possibility would be to make SentenceBuilder non-abstract, move the default implementations there from DefaultSentenceBuilder, and then get rid of DefaultSentenceBuilder altogether.

[moh-hassan]

Is there a reason that DefaultSentenceBuilder is marked private?

DefaultSentenceBuilder is a nested private class for the class SentenceBuilder.
Nested types default to private; they are accessible only from their containing type.
Although it can be public, it will be accessed as:

     public class MySentenceBuilder: SentenceBuilder.DefaultSentenceBuilder
     {
       //.....
    }

and cause breaking API.

It's preferred to inherit from the public abstract class SentenceBuilder

Another possibility would be to make SentenceBuilder non-abstract, ...

This can break the public API of the library. It's used by the localized demo

[asherber]

Sorry, I wasn't clear. My question was whether there was a design reason for not making DefaultSentenceBuilder a public class in the first place.

If this class were moved into its own file and turned into its own public class, I don't think that would be a breaking change -- the class is currently not visible, so adding it as a visible class wouldn't affect anyone's current usage.

The problem with inheriting from the abstract SentenceBuilder is that I would have to provide implementations for all of its properties, whereas inheriting from DefaultSentenceBuilder lets me override only the behavior I want to change, which is much simpler (as in my example above). I think this would be much friendler for users of the library.

(There's another workaround that involves grabbing a copy of DefaultSentenceBuilder before setting Factory and then delegating to that copy in order to inherit behavior, but it's still more work than just inheriting from DefaultSentenceBuilder.)