To create a copy of a constraint, with a different multiplier

NSLayoutConstraint+Multiplier.swift

//
//  NSLayoutConstraint+Multiplier.swift
//
//  Created by Rigoberto Sáenz Imbacuán (https://www.linkedin.com/in/rsaenzi/)
//  Copyright © 2017. All rights reserved.
//

extension NSLayoutConstraint {

   @discardableResult
   static func change(_ constraint: NSLayoutConstraint, newMultiplier: CGFloat) -> NSLayoutConstraint {
      // Creates a copy of the constraint
      let newConstraint = NSLayoutConstraint(
         item: constraint.firstItem,
         attribute: constraint.firstAttribute,
         relatedBy: constraint.relation,
         toItem: constraint.secondItem,
         attribute: constraint.secondAttribute,
         multiplier: newMultiplier,
         constant: constraint.constant
      )

      newConstraint.priority = constraint.priority

      // Then switch them
      NSLayoutConstraint.deactivate([constraint])
      NSLayoutConstraint.activate([newConstraint])

      return newConstraint
   }

   static func trailing(_ view: UIView, to item: UIView) -> NSLayoutConstraint {
      let trailing = NSLayoutConstraint (
         item: view,
         attribute: .trailing,
         relatedBy: .equal,
         toItem: item,
         attribute: .trailing,
         multiplier: 1,
         constant: 0
      )

      return trailing
   }
}