ArrayExtensions.swift

public extension Array where Element: Equatable {
    
    func find(other: Element) -> Element? {
        for element in self {
            if element == other {
                return element
            }
        }
        return nil
    }
    
    mutating func toggleElement(element: Element) {
        if let hasIndex = self.indexOf(element) {
            self.removeAtIndex(hasIndex)
        }
        else {
            self.append(element)
        }
    }
}