Convenience UILayoutPriority extension for more declarative content hugging (and compression resistance) definition

UILayoutPriority.swift

import UIKit
import PlaygroundSupport

let view = UIView(frame: CGRect(x: 0, y: 0, width: 414, height: 100))
view.backgroundColor = .white

let titleLabel = UILabel()
titleLabel.text = "Hello"
titleLabel.backgroundColor = .purple
view.addSubview(titleLabel)

let subtitleLabel = UILabel()
subtitleLabel.text = "It's me"
subtitleLabel.backgroundColor = .yellow
view.addSubview(subtitleLabel)

titleLabel.translatesAutoresizingMaskIntoConstraints = false
subtitleLabel.translatesAutoresizingMaskIntoConstraints = false

extension UILayoutPriority {
  static func + (lhs: UILayoutPriority, rhs: Float) -> UILayoutPriority {
    return UILayoutPriority(lhs.rawValue + rhs)
  }

  static func - (lhs: UILayoutPriority, rhs: Float) -> UILayoutPriority {
    return UILayoutPriority(lhs.rawValue - rhs)
  }
}

extension UILayoutPriority: Comparable {
  public static func < (lhs: UILayoutPriority, rhs: UILayoutPriority) -> Bool {
    return lhs.rawValue < rhs.rawValue
  }
}

extension UIView {
  func setContentHuggingPriority(for axis: UILayoutConstraintAxis, lowerThan view: UIView) {
    setContentHuggingPriority(for: axis, lowerThan: [view])
  }

  func setContentHuggingPriority(for axis: UILayoutConstraintAxis, lowerThan views: [UIView]) {
    guard let minimumPriority = views.map({ $0.contentHuggingPriority(for: axis) }).min() else {
      preconditionFailure()
    }

    setContentHuggingPriority(minimumPriority - 1, for: axis)
  }
}

NSLayoutConstraint.activate([
  titleLabel.topAnchor.constraintEqualToSystemSpacingBelow(view.topAnchor, multiplier: 0),
  titleLabel.leadingAnchor.constraintEqualToSystemSpacingAfter(view.leadingAnchor, multiplier: 0),
  titleLabel.bottomAnchor.constraintEqualToSystemSpacingBelow(view.bottomAnchor, multiplier: 0),

  titleLabel.trailingAnchor.constraintEqualToSystemSpacingAfter(
    subtitleLabel.leadingAnchor,
    multiplier: 0
  ),

  subtitleLabel.topAnchor.constraintEqualToSystemSpacingBelow(view.topAnchor, multiplier: 0),
  subtitleLabel.bottomAnchor.constraintEqualToSystemSpacingBelow(view.bottomAnchor, multiplier: 0),
  subtitleLabel.trailingAnchor.constraintEqualToSystemSpacingAfter(
    view.trailingAnchor,
    multiplier: 0
  ),
])
subtitleLabel.setContentHuggingPriority(for: .horizontal, lowerThan: titleLabel)

PlaygroundPage.current.liveView = view