Virtual proxy pattern

WeakReference.swift

final class WeakReference<T: AnyObject> {
    weak var ref: T?

    init (_ object: T) {
        self.ref = object
    }
}

extension WeakReference: CurrencyPresenterOutput where T: CurrencyPresenterOutput {
    func present(_ currency: CurrencyPresenterModel) {
        ref?.present(currency)
    }
}