How to avoid an anonymous closure in lazy properties

LazyLoadable.swift

/*
lazy var actionButton: UIButton = UIButton().add(to: view) { btn in
    // button configuration
}

instead of:

lazy var actionButton: UIButton = {
    let btn = UIButton()
    addSubview(btn)
    // button configuration
    return btn
}()
*/

public protocol LazyLoadable {}
extension NSObject: LazyLoadable {}

public extension LazyLoadable {
    func didLoad(_ completion: (Self) -> Void) -> Self {
        completion(self); return self
    }
    /// Kotlin-like convenience accessor to instance
    func `let`(_ closure: (Self) -> Void) -> Self {
        closure(self); return self
    }
}

#if canImport(QuartzCore)
import QuartzCore

public extension LazyLoadable where Self: CALayer {
    func add(to superlayer: CALayer) -> Self {
        superlayer.addSublayer(self); return self
    }
    func add(to superlayer: CALayer, completion: (Self) -> Void) -> Self {
        superlayer.addSublayer(self); completion(self); return self
    }
}
#endif

#if canImport(UIKit)
import UIKit

public extension LazyLoadable where Self: CALayer {
    func insert(to superview: UIView, at index: UInt32) -> Self {
        superview.layer.insertSublayer(self, at: index); return self
    }
    func insert(to superview: UIView, at index: UInt32, completion: (Self) -> Void) -> Self {
        superview.layer.insertSublayer(self, at: index); completion(self); return self
    }
    func insert(to superview: UIView, above: CALayer, completion: (Self) -> Void) -> Self {
        superview.layer.insertSublayer(self, above: above); completion(self); return self
    }
    func insert(to superview: UIView, below: CALayer, completion: (Self) -> Void) -> Self {
        superview.layer.insertSublayer(self, below: below); completion(self); return self
    }
    func add(to superview: UIView) -> Self {
        superview.layer.addSublayer(self); return self
    }
    func add(to superview: UIView, completion: (Self) -> Void) -> Self {
        superview.layer.addSublayer(self); completion(self); return self
    }
}

public extension LazyLoadable where Self: UIView {
    func add(to superview: UIView) -> Self {
        superview.addSubview(self); return self
    }
    func add(to superview: UIView, completion: (Self) -> Void) -> Self {
        superview.addSubview(self); completion(self); return self
    }
    func insert(to superview: UIView, above: UIView, completion: (Self) -> Void) -> Self {
        superview.insertSubview(self, aboveSubview: above); completion(self); return self
    }
    func insert(to superview: UIView, below: UIView, completion: (Self) -> Void) -> Self {
        superview.insertSubview(self, belowSubview: below); completion(self); return self
    }
    func add(to superview: UIView?) -> Self {
        superview?.addSubview(self); return self
    }
    func add(to superview: UIView?, completion: (Self) -> Void) -> Self {
        superview?.addSubview(self); completion(self); return self
    }
    func insert(to superview: UIView?, above: UIView, completion: (Self) -> Void) -> Self {
        superview?.insertSubview(self, aboveSubview: above); completion(self); return self
    }
    func insert(to superview: UIView?, below: UIView, completion: (Self) -> Void) -> Self {
        superview?.insertSubview(self, belowSubview: below); completion(self); return self
    }
    func insert(to superview: UIView?, at index: Int, completion: (Self) -> Void) -> Self {
        superview?.insertSubview(self, at: index); completion(self); return self
    }
}
public extension LazyLoadable where Self: UILayoutGuide {
    func add(to superview: UIView) -> Self {
        superview.addLayoutGuide(self); return self
    }
    func add(to superview: UIView, completion: (Self) -> Void) -> Self {
        completion(add(to: superview)); return self
    }
}

public extension LazyLoadable where Self: UIViewController {
    func add(to superController: UIViewController) -> Self {
        superController.add(child: self)
        return self
    }
    func add(to superController: UIViewController, completion: (Self) -> Void) -> Self {
        completion(add(to: superController)); return self
    }
}
#endif

#if os(macOS)
import AppKit

public extension LazyLoadable where Self: CALayer {
    func insert(to superview: NSView, at index: UInt32) -> Self {
        superview.layer?.insertSublayer(self, at: index); return self
    }
    func insert(to superview: NSView, at index: UInt32, completion: (Self) -> Void) -> Self {
        superview.layer?.insertSublayer(self, at: index); completion(self); return self
    }
    func insert(to superview: NSView, above: CALayer, completion: (Self) -> Void) -> Self {
        superview.layer?.insertSublayer(self, above: above); completion(self); return self
    }
    func insert(to superview: NSView, below: CALayer, completion: (Self) -> Void) -> Self {
        superview.layer?.insertSublayer(self, below: below); completion(self); return self
    }
    func add(to superview: NSView) -> Self {
        superview.layer?.addSublayer(self); return self
    }
    func add(to superview: NSView, completion: (Self) -> Void) -> Self {
        superview.layer?.addSublayer(self); completion(self); return self
    }
}

public protocol _SubviewsContainer {
    var __contentView: NSView { get }
}
extension NSView: _SubviewsContainer {
    public var __contentView: NSView { self }
}
extension NSViewController: _SubviewsContainer {
    public var __contentView: NSView { view }
}

public extension LazyLoadable where Self: NSView {
    func add<C>(to superview: C) -> Self where C: _SubviewsContainer {
        superview.__contentView.addSubview(self); return self
    }
    func add<C>(to superview: C, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview.__contentView.addSubview(self); completion(self); return self
    }
    func insert<C>(to superview: C, above: NSView, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview.__contentView.addSubview(self, positioned: .above, relativeTo: above); completion(self); return self
    }
    func insert<C>(to superview: C, below: NSView, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview.__contentView.addSubview(self, positioned: .below, relativeTo: below); completion(self); return self
    }
    func add<C>(to superview: C?) -> Self where C: _SubviewsContainer {
        superview?.__contentView.addSubview(self); return self
    }
    func add<C>(to superview: C?, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview?.__contentView.addSubview(self); completion(self); return self
    }
    func insert<C>(to superview: C?, above: NSView, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview?.__contentView.addSubview(self, positioned: .above, relativeTo: above); completion(self); return self
    }
    func insert<C>(to superview: C?, below: NSView, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        superview?.__contentView.addSubview(self, positioned: .below, relativeTo: below); completion(self); return self
    }
    func insert<C>(to superview: C?, at index: Int, completion: (Self) -> Void) -> Self where C: _SubviewsContainer {
        guard let sView = superview?.__contentView else { completion(self); return self }
        if sView.subviews.count > index {
            sView.addSubview(self, positioned: .below, relativeTo: sView.subviews[index])
        } else {
            sView.addSubview(self)
        }
        completion(self)
        return self
    }
}
@available(macOS 10.11, *)
public extension LazyLoadable where Self: NSLayoutGuide {
    func add(to superview: NSView) -> Self {
        superview.addLayoutGuide(self); return self
    }
    func add(to superview: NSView, completion: (Self) -> Void) -> Self {
        completion(add(to: superview)); return self
    }
}

#endif