>>29That doesn't make it an influence. I'm sure he's also used one or more of: Lisp, PHP, Forth, Java, Tcl and so on, but I don't see their influence either.
In fact, the most likely resemblance to Go, protocols (vs. interfaces), more closely resembles virtually every other language with this kind of lateral subtyping feature (protocols, traits, roles, etc.) In Go, interfaces are structurally typed¹, but protocols in Swift are opt-in². Swift, Java, Rust, Perl, Perl 6, and PHP are all in that category and you admit mixins that adds Ruby, Factor and I believe CLOS. You get the idea.
1.
https://en.wikipedia.org/wiki/Structural_typing2.
https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Protocols.html#//apple_ref/doc/uid/TP40014097-CH25-XID_345I think he might have been influenced to avoid Go's idiosyncrasies. What they have in common seems to be mostly: has curlies, signatures, a type system. Types aren't even annotated by juxtaposition (thank god). I can't think of a single significant similarity and I suspect he might have even gone out of his way to avoid it.