Lightweight DSL for defining UIView hierarchy using Swift 5.1's function builders.

UIViewHierarchyBuilder.swift

protocol UIViewArrayConvertible {
    func items() -> [UIView]
}
extension UIView: UIViewArrayConvertible {
    func items() -> [UIView] { [self] }
}
extension Array: UIViewArrayConvertible where Element: UIView {
    func items() -> [UIView] { self }
}

@_functionBuilder
struct UIViewBuilder {
    
    static func buildBlock(_ components: UIViewArrayConvertible ...) -> UIViewArrayConvertible { components.flatMap { $0.items() } }
    
    static func buildIf(_ component: UIViewArrayConvertible?) -> UIViewArrayConvertible { component ?? [UIView]() }
    
    static func buildEither(first: UIViewArrayConvertible) -> UIViewArrayConvertible { first }
    
    static func buildEither(second: UIViewArrayConvertible) -> UIViewArrayConvertible { second }

}

extension UIView {
    
    @discardableResult
    func addSubviews(@UIViewBuilder _ viewBuilder: () -> UIViewArrayConvertible) -> UIView {
        for view in viewBuilder().items() {
            self.addSubview(view)
        }
        return self
    }
    
}

extension UIViewController {
    
    @discardableResult
    func addSubviews(@UIViewBuilder _ viewBuilder: () -> UIViewArrayConvertible) -> UIView {
        for view in viewBuilder().items() {
            self.view.addSubview(view)
        }
        return self.view
    }
    
}

Usage example:

self.view.addSubviews {
    self.background
    self.container.addSubviews {
        self.icon
        self.labelsContainer.addSubviews {
            self.title
            self.subTitle
        }
        if self.isFavorite {
            self.starFilledIndicator
        } else {
            self.starStrokedIndicator
        }
        self.button
    }
}