if FEATURE_FLAG_ENABLED(): do_new_version() else: do_old_version() all throughout code. "FEATURE_FLAG_ENABLED()" could be checking a database

if FEATURE_FLAG_ENABLED(): do_new_version() else: do_old_version() all throughout code. "FEATURE_FLAG_ENABLED()" could be checking a database or an external service. I've also seen it done through environment variables, but I don't like that pattern as much.