Example to show object pool design pattern

object-pool.swift

enum PaymentMethod {
    case creditCard
    case debitCard
    case wallet
    case cash
}

protocol PaymentPresenterStrategy {}

protocol MethodsPresenterResolvable {
    func register(methods: [PaymentMethod])
    func resolvePresenter(for method: PaymentMethod) -> PaymentPresenterStrategy?
}

final class MethodsPresenterResolver: MethodsPresenterResolvable {
    private var presenterCache: [PaymentMethod: PaymentPresenterStrategy]?
    
    func register(methods: [PaymentMethod]) {
        var cache = [PaymentMethod: PaymentPresenterStrategy]()
        
        for method in methods {
            guard let paymentPresenter = presenter(for: method) else {
                continue
            }
            cache[method] = paymentPresenter
        }
        
        presenterCache = cache
    }
    
    func resolvePresenter(for method: PaymentMethod) -> PaymentPresenterStrategy? {
        return presenterCache?[method]
    }
    
    private func presenter(for method: PaymentMethod) -> PaymentPresenterStrategy? {
        switch method {
        case .creditCard:
            return CreditCardPresenter()
        case .debitCard:
            return DebitCardPresenter()
        case .wallet:
            return WalletPresenter()
        case .cash:
            return CashPresenter()
        }
    }
}

final class CreditCardPresenter: PaymentPresenterStrategy {}

final class DebitCardPresenter: PaymentPresenterStrategy {}

final class WalletPresenter: PaymentPresenterStrategy {}

final class CashPresenter: PaymentPresenterStrategy {}