         if (self & ConstraintAttributes.Width) {
             attrs.append(.Width)
         }
-        if (self & ConstraintAttributes.Height ){
+        if (self & ConstraintAttributes.Height) {
             attrs.append(.Height)
         }
         if (self & ConstraintAttributes.CenterX) {

        return attrs
    }
}
@assignment func += (inout left: ConstraintAttributes, right: ConstraintAttributes) {
    left = (left | right)
}
@assignment func -= (inout left: ConstraintAttributes, right: ConstraintAttributes) {
    left = ConstraintAttributes(left.toRaw() & ~right.toRaw())
}

/**

    
    func install() -> Array<LayoutConstraint> {
        var installOnView: View? = nil
        if self.toItem.view != nil {
            installOnView = Constraint.closestCommonSuperviewFromView(self.fromItem.view, toView: self.toItem.view)
            if installOnView == nil {
                NSException(name: "Cannot Install Constraint", reason: "No common superview between views", userInfo: nil).raise()
                return []
            }
        } else {
            installOnView = self.fromItem.view?.superview
            if installOnView == nil {
                NSException(name: "Cannot Install Constraint", reason: "Missing superview", userInfo: nil).raise()
                return []
            }
