"Higher-ranked type alias" isn't entirely right here, but its good to think about the type theory. What you have on RHS is a prenex (rank-0) polymorphic type, and the type alias itself is still in prenex form. You would need e.g., for<'a> fn(fn(&'a u8)) to have a rank-1 type, which would indeed be higher ranked.
I've (hopefully) corrected the post in this regard, by switching from "higher-ranked type alias" to "type alias to a polymorphic function pointer type". The changeset can be seen here.
Mazdak Farrokhzad
"Higher-ranked type alias" isn't entirely right here, but its good to think about the type theory. What you have on RHS is a prenex (rank-0) polymorphic type, and the type alias itself is still in prenex form. You would need e.g.,
for<'a> fn(fn(&'a u8))to have a rank-1 type, which would indeed be higher ranked.