         return _value != nil
     }
     
+    override public var claimedValues: Int {
+        return _value != nil ? 1 : 0
+    }
+    
     override func setValue(values: [String]) -> Bool {
         if values.count == 0 {
             return false

     * - parameter options: An array containing the options to set.
     */
    public func setOptions(options: [Option]) {
        _options = options
    }
    
    /**

        return s
    }
}

#if os(Linux)
    /**
     *  Returns `true` iff `self` begins with `prefix`.
     *
     *  A basic implementation of `hasPrefix` for Linux.
     *  Should be removed once a proper `hasPrefix` patch makes it to the Swift 2.2 development branch.
     */
    extension String {
        func hasPrefix(prefix: String) -> Bool {
            if prefix.isEmpty {
                return false
            }
            
            let c = self.characters
            let p = prefix.characters
            
            if p.count > c.count {
                return false
            }
            
            for (c, p) in zip(c.prefix(p.count), p) {
                guard c == p else {
                    return false
                }
            }
            
            return true
        }
        
        /**
         *  Returns `true` iff `self` ends with `suffix`.
         *
         *  A basic implementation of `hasSuffix` for Linux.
         *  Should be removed once a proper `hasSuffix` patch makes it to the Swift 2.2 development branch.
         */
        func hasSuffix(suffix: String) -> Bool {
            if suffix.isEmpty {
                return false
            }
            
            let c = self.characters
            let s = suffix.characters
            
            if s.count > c.count {
                return false
            }
            
            for (c, s) in zip(c.suffix(s.count), s) {
                guard c == s else {
                    return false
                }
            }
            
            return true
        }
    }
#endif


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