gistfile1.txt

import UIKit

struct ConstraintInfo {
    var attribute: NSLayoutAttribute = .left
    var secondAttribute: NSLayoutAttribute = .notAnAttribute
    var constant: CGFloat = 0
    var identifier: String?
    var relation: NSLayoutRelation = .equal
}

precedencegroup constPrecedence {
    associativity: left
    higherThan: AssignmentPrecedence
}

infix operator >>>- : constPrecedence

@discardableResult
func >>>- <T: UIView> (left: (T, T), block: (inout ConstraintInfo) -> ()) -> NSLayoutConstraint {
    var info = ConstraintInfo()
    block(&info)
    info.secondAttribute = info.secondAttribute == .notAnAttribute ? info.attribute : info.secondAttribute
    
    let constraint = NSLayoutConstraint(item: left.1,
                                        attribute: info.attribute,
                                        relatedBy: info.relation,
                                        toItem: left.0,
                                        attribute: info.secondAttribute,
                                        multiplier: 1,
                                        constant: info.constant)
    constraint.identifier = info.identifier
    left.0.addConstraint(constraint)
    return constraint
}

protocol GestureControlDelegate {
    func gestureControlDidSwipe(direction: UISwipeGestureRecognizerDirection)
}

class GestureControl: UIView {
    
    let delegate: GestureControlDelegate
    
    init(view: UIView, delegate: GestureControlDelegate) {
        self.delegate = delegate
        
        super.init(frame: CGRect.zero)
        
        let swipeLeft       = UISwipeGestureRecognizer(target: self, action: #selector(swipeHandler(gesture:)))
        swipeLeft.direction = .left
        addGestureRecognizer(swipeLeft)
        
        let swipeRight       = UISwipeGestureRecognizer(target: self, action: #selector(swipeHandler(gesture:)))
        swipeRight.direction = .right
        addGestureRecognizer(swipeRight)
        
        translatesAutoresizingMaskIntoConstraints = false
        backgroundColor                           = .clear
        
        view.addSubview(self)

        for attribute: NSLayoutAttribute in [.left, .right, .top, .bottom] {
            (view, self) >>>- {
                $0.attribute = attribute
            }
        }
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

extension GestureControl {
    
    dynamic func swipeHandler(gesture: UISwipeGestureRecognizer) {
        delegate.gestureControlDidSwipe(direction: gesture.direction)
    }
}