a.swift

import Foundation
import UIKit

class ViewPool {
    private var freeViews: [UIView] = []
    private var allViews: [UIView] = []

    init() {
    }

    private func availableView() -> UIView {
        if let view = freeViews.popLast() {
            return view
        }
        let view = UIView()
        allViews.append(view)
        return view
    }

    func acquireView() -> PoolView {
        return PoolView(view: availableView(), pool: self)
    }

    func releaseView(view: UIView) {
        freeViews.append(view)
    }
}




import Foundation
import UIKit

class PoolView {
    private let view: UIView
    private let pool: ViewPool

    init(view: UIView, pool: ViewPool) {
        self.view = view
        self.pool = pool
    }

    deinit {
        reset()
        pool.releaseView(view: view)
    }

    func reset() {
        frame = .zero
        backgroundColor = nil
    }

    func addToSuperview(_ superview: UIView) {
        superview.addSubview(view)
    }

    func removeFromSuperview() {
        view.removeFromSuperview()
    }

    var backgroundColor: UIColor? {
        get {
            return view.backgroundColor
        }
        set {
            view.backgroundColor = newValue
        }
    }

    var frame: CGRect {
        get {
            return view.frame
        }
        set {
            view.frame = newValue
        }
    }
}


// Test code...


import UIKit

class ViewController: UIViewController {

    let pool: ViewPool = ViewPool()

    lazy var greenView: PoolView? = pool.acquireView()

    override func viewDidLoad() {
        super.viewDidLoad()
        if let greenView = greenView {
            greenView.backgroundColor = .green
            greenView.frame = CGRect(x: 20, y: 20, width: 100, height: 100)
            greenView.addToSuperview(view)
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            if let greenView = self.greenView {
                greenView.removeFromSuperview()
            }
            self.greenView = nil
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            self.greenView = self.pool.acquireView()
            if let greenView = self.greenView {
                greenView.backgroundColor = .purple
                greenView.frame = CGRect(x: 20, y: 20, width: 200, height: 200)
                greenView.addToSuperview(self.view)
            }
        }
    }
}