UIView extension that makes it easier to write auto layout constraints

UIView+inset+next.swift

import UIKit

extension UIView {
    func inset(into view: UIView, allSides: CGFloat = 0) -> [NSLayoutConstraint] {
        inset(into: view, horizontal: allSides, vertical: allSides)
    }

    func inset(into view: UIView, horizontal: CGFloat? = nil, vertical: CGFloat? = nil) -> [NSLayoutConstraint] {
        inset(into: view, leading: horizontal, trailing: horizontal, top: vertical, bottom: vertical)
    }

    func inset(
        into view: UIView,
        leading: CGFloat? = nil,
        trailing: CGFloat? = nil,
        top: CGFloat? = nil,
        bottom: CGFloat? = nil
    ) -> [NSLayoutConstraint] {
        var constraints = [NSLayoutConstraint]()

        if let leading = leading {
            constraints.append(leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: leading))
        }

        if let trailing = trailing {
            constraints.append(trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -trailing))
        }

        if let top = top {
            constraints.append(topAnchor.constraint(equalTo: view.topAnchor, constant: top))
        }

        if let bottom = bottom {
            constraints.append(bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -bottom))
        }

        return constraints
    }

    func next(to view: UIView, horizontal: CGFloat? = nil, vertical: CGFloat? = nil) -> [NSLayoutConstraint] {
        var constraints = [NSLayoutConstraint]()

        if let horizontal = horizontal {
            constraints.append(leadingAnchor.constraint(equalTo: view.trailingAnchor, constant: horizontal))
        }

        if let vertical = vertical {
            constraints.append(topAnchor.constraint(equalTo: view.bottomAnchor, constant: vertical))
        }

        return constraints
    }
}

This allows me to write:

titleLabel.inset(into: view, leading: 16, trailing: 16, top: 16) +
    descriptionLabel.inset(into: view, horizontal: 16) +
    descriptionLabel.next(to: titleLabel, vertical: 8) +
    stackView.inset(into: view, leading: 16, trailing: 16, bottom: 16) +
    stackView.next(to: descriptionLabel, vertical: 16)

Instead of:

[
    titleLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16),
    titleLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16),
    titleLabel.topAnchor.constraint(equalTo: view.topAnchor, constant: 16),

    descriptionLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16),
    descriptionLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16),
    descriptionLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 16),

    stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16),
    stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16),
    stackView.topAnchor.constraint(equalTo: descriptionLabel.bottomAnchor, constant: 16),
    stackView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -16)
]