I think that probably in Swift each individual string is required to be of finite length, as in most programming languages. The set of finite (but arbitrary) le

I think that probably in Swift each individual string is required to be of finite length, as in most programming languages. The set of finite (but arbitrary) length strings drawn from a finite set of characters is countable. On the other hand this type BitSequence (pretending UInt contains all non-negative sequences) is the set of all countable infinite sequences of bits. That set, as you explained, has the cardinality of the continuum.