activate(
  lineBlock.anchor.left.bottom
)

// later
activate(
  firstSquareBlock.anchor.left.equal.to(lineBlock.anchor.right),
  firstSquareBlock.anchor.bottom
)

// later
activate(
  secondSquareBlock.anchor.right.bottom
)

activate(
  c.anchor.left,
  b.anchor.right,
  c.anchor.top.bottom,
  c.anchor.top.bottom.width.apply(to: [d, e, f, g, a, b]),
  c.anchor.fixedSpacingHorizontally(togetherWith: [d, e, f, g, a, b], spacing: 0)
)

activate(
  cd.anchor.top,
  cd.anchor.size.equal.to(c.anchor.size).multiplier(2/3),
  cd.anchor.top.size.apply(to: [de, fg, ga, ab]),
  cd.anchor.centerX.equal.to(c.anchor.right),
  de.anchor.centerX.equal.to(d.anchor.right),
  fg.anchor.centerX.equal.to(f.anchor.right),
  ga.anchor.centerX.equal.to(g.anchor.right),
  ab.anchor.centerX.equal.to(a.anchor.right)
)

let view = UIView()
view.anchor.left.right

let guide = UILayoutGuide()
guide.anchor.width.height

topLayoutGuide.anchor.bottom
bottomLayoutGuide.anchor.top

activate(
  a.anchor.top.left,
  b.anchor.top.right,
  c.anchor.bottom.left,
  d.anchor.bottom.right
)

anchor.top.left.bottom.right
  .leading.trailing
  .topMargin.bottomMargin.leftMargin.rightMargin
  .centerX.centerY
  .centerXWithinMargins.centerXWithinMargins
  .lastBaseline.firstBaseline
  .width.height

a.anchor.top.equal.to(b.bottom)
a.anchor.width.greaterThanOrEqual.to(b.anchor.height)
a.anchor.width.lessThanOrEqual.to(b.anchor)

a.anchor.top.equal.to(b.anchor.bottom)
  .constant(10).multiplier(1.5).priority(999)
  .id("verticalSpacingBetweenA-B")

var constraint: NSLayoutConstraint?
activate(
  view.anchor.center.constant(10).ref({ constraint = $0.first })
)

a.anchor.center  // centerX, centerY
a.anchor.size  // width, height
a.anchor.edges  // top, right, bottom, left

a.anchor.edges.insets(EdgeInsets(top: 1, left: 2, bottom: 3, right: 4))  // top+1, left+2, bottom+3, right+4
a.anchor.edges.insets(5)  // top+5, left+5, bottom-5, right-5

a.anchor.paddingHorizontally(20) // leading+20, trailing-20
b.anchor.paddingVertically(20)	// top+20, bottom-20

a.anchor.height.equal.to(b.anchor.width)
c.anchor.size.equal.to(d.anchor)

a.anchor.height.equal.to(20)  // height==20
b.anchor.size.equal.to(20)  // width==20, height==20

c.anchor.width.constant(20)  // width==superview.width+20

a.anchor.height.equal.to(a.anchor.width)  // height==width

a.anchor.width.constant(10)
a.anchor.height.ratio(2) // height==width*2

a.anchor.height.constant(10)
a.anchor.width.ratio(2) // width==height*2

a.anchor.top.left // a.top == a.superview.top, a.left == a.superview.left

a.anchor.top.bottom.width.equal.to(b.anchor) // a.top == b.top, a.bottom == b.bottom, a.width == b.width

a.anchor.find(.height)?.constant = 100

// later
b.anchor.find(.height)?.constant = 100

// later
c.anchor.find(.height)?.constant = 100

// Change constraint
a.anchor.find(.height)?.constant = 100
loginButtonHeightConstraint.isActive = false

let animator = UIViewPropertyAnimator(duration: 1, dampingRatio: 0.7)
animator.addAnimations { [weak self] in
  self?.view.layoutIfNeeded()
}

animator.startAnimation(afterDelay: 1)

func toggle(_ group: Group) {
  [g1, g2, g3, g4].forEach { g in
    guard let g = g else {
      return
    }

    g.isActive = (g == group)
  }
}

g1 = group(a.anchor.top.left)
g2 = group(a.anchor.top.right)
g3 = group(a.anchor.bottom.right)
g4 = group(a.anchor.bottom.left)

g1.isActive = true

animator = Animator(view: self, animations: [
  {
    self.toggle(self.g2)
  },
  {
    self.toggle(self.g3)
  },
  {
    self.toggle(self.g4)
  },
  {
    self.toggle(self.g1)
  }
  ])

animator.start()

public protocol ConstraintProducer {
  func constraints() -> [NSLayoutConstraint]
}

// This accepts a list of views, and build constraints
class MyAwesomeLayout: ConstraintProducer {
  init(views: [UIView]) {
    // Your code goes here
  }

  func constraints() -> [NSLayoutConstraint] {
    // Your code goes here
    return []
  }
}

let awesomeLayout = MyAwesomeLayout(views: [view1, view2])
activate(awesomeLayout)

a.anchor.left.height.apply(to: [b, c]),

addSubview(scrollView)
[a, b, c, d].forEach {
  scrollView.addSubview($0)
}

activate(
  scrollView.anchor.edges.insets(8),
  a.anchor.pagingHorizontally(togetherWith: [b, c, d], in: scrollView)
)

activate(
  container.anchor.edges.insets(8),
  a.anchor.left.top.bottom,
  c.anchor.right,
  a.anchor.top.bottom.width.apply(to: [b, c]),
  a.anchor.fixedSpacingHorizontally(togetherWith: [b, c], spacing: 50)
)

activate(
  container.anchor.edges.insets(8),
  a.anchor.size.equal.to(30),
  b.anchor.size.equal.to(30),
  c.anchor.size.equal.to(30),
  a.anchor.left.centerY,
  a.anchor.centerY.apply(to: [b, c]),
  c.anchor.right,
  a.anchor.dynamicSpacingHorizontally(togetherWith: [b, c])
)