LanguageBase and LanguageService

[grokys]

The LanguageBase class derives from LanguageService and the docs for LanguageService say:

Derive a class from this class to create your own language service. You must also, at the very least, implement a parser that implements the IScanner interface. All features of a language service are based on this parser.

However LanguageBase just returns null for the scanner. Isn't this a breach of the contract for LanguageService?

[reduckted]

Isn't this a breach of the contract for LanguageService?

Not according to the documentation for GetScanner:

If successful, returns an IScanner object; otherwise, returns a null value.

So null is a valid return value, and that base class can't return anything else because it doesn't know what type of scanner to create.

Perhaps it would be better if the base class declared that method as abstract.

[grokys]

I assume that if "at the very least you must implement an IScanner" but creating the scanner fails, then the LanguageService is considered invalid?

[grokys]

Another point of confusion for me here is that in the Language Service and Editor Extension Points documentation, LanguageService isn't mentioned, and other MEF based solutions are suggested for doing the things that LanguageBase seems to do (content types, file extensions etc).