[ak_111]

As poster dead deep in the thread below, something like this can happen

doc_format = get_user_input() parsed_doc = foolib.parse(doc_format)

You as the implementer might know the user will never input xml, so doc_format can't be 'xml' (you might even add some error handling if the user inputs this), but how can you communicate this to the compiler?

[arccy]

That's called bad library design. Rather than a global, make an instantiated parser that takes in specific codecs.

[tester756]

It aint matter, if format is comes from runtime then compiler will not know.