Add non-updating insert methods to swift Set

gistfile1.txt

import Foundation

extension Set {

    mutating func nonUpdatingInsert(member: Element) {
        if !self.contains(member) {
            self.insert(member)
        }
    }
    
    mutating func nonUpdatingUnionInPlace<S : SequenceType where S.Generator.Element == Element>(sequence: S) {
        for item in sequence {
            if !self.contains(item) {
                self.insert(item)
            }
        }
    }
}

Official insert method is actually an upsert. See http://www.chaonis.com/2016/01/swift-set-vs-nsmutableset/
This is a quick fix for those who want a non updating version.