Tuples cannot conform to protocols or be extended because they are compound types. Is it correct to say that this is true because there is not a unique metatype for compound types? IOW, there is no unique existential container thingy for a tuples? (Not sure if I am using the proper vocabulary here or not.)
The way I’ve seen this explained is that tuples are "structural types" (their compatibility is determined by their structure) and other types are "nominal types" (they can be named, and their compatibility is determined by that name).