Buttons with equal width using Visual Format Language

AutoLayout.swift

import UIKit

public extension UIView {
    
    var autoLayout: AutoLayout {
        
        return AutoLayout(self)
    }
}

public struct AutoLayout {
    
    public let base: UIView
    
    public init(_ base: UIView) {
        
        self.base = base
    }
    
    public func applyVisualFormatLanguage(constraints: [String],
                                          options: NSLayoutConstraint.FormatOptions = [],
                                          metrics: [String: Any]? = nil) {
        
        base.translatesAutoresizingMaskIntoConstraints = false
        var views = enumerateSubViews()
        views["baseView"] = base
        views.values.forEach { $0.translatesAutoresizingMaskIntoConstraints = false }
        constraints.forEach {

            base.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: $0, options: options, metrics: metrics, views: views))
        }
    }
    
    public func enumerateSubViews() -> [String: UIView] {
        
        var views = [String: UIView]()
        let mirror = Mirror(reflecting: base)

        let addToViewsClosure: ((Mirror.Child) -> Void) = { child in

            child.label.flatMap { label in

                let key = label.replacingOccurrences(of: ".storage", with: "")
                views[key] = child.value as? UIView
            }
        }

        mirror.children.forEach(addToViewsClosure)
        mirror.superclassMirror?.children.forEach(addToViewsClosure)

        return views
    }
}

Foo.swift

final class Foo: LayoutView {
    
    private let login = UIButton()
    private let register = UIButton()
    
    override func layout() {
        
        super.layout()
        autoLayout.applyVisualFormatLanguage(constraints: [
            "H:[login(==register)]"
        ])
    }
}

LayoutView.swift

import UIKit

class LayoutView: UIView {
    
    override init(frame: CGRect) {
        
        super.init(frame: frame)
        layout()
    }
    
    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        
        super.init(coder: aDecoder)
        layout()
    }
    
    func layout() {

        autoLayout.enumerateSubViews().values.forEach { addSubview($0) }
    }
}