A dispose bag that keeps only one disposable in the bag at a time.

SingleDisposer.swift

import Foundation
import RxSwift

extension Disposable {
    /// Adds `self` to `single`
    ///
    /// - parameter single: `SingleDisposer` to add `self` to.
    /// - note: `SingleDisposer` is a wrapper of `DisposeBag` that is recreated
    /// whenever a disposable object is inserted into it, cancelling any
    /// previous subscriptions. It keeps at most one subscription at a
    /// time in memory.
    /// `SingleDisposer` releases subscriptions on deinit.
    public func disposed(by single: SingleDisposer) {
        single.insert(self)
    }
}

/// `SingleDisposer` is a wrapper of `DisposeBag` that is recreated
/// whenever a disposable object is inserted into it, cancelling any
/// previous subscription. It keeps at most one subscription at a
/// time in memory.
/// `SingleDisposer` releases subscriptions on deinit.
public final class SingleDisposer: Disposable {
    private var bag: DisposeBag?
    
    public init() {}
    
    /// Dispose current subscription.
    public func dispose() {
        bag = nil
    }
    
    /// Cancels any previous subscription before inserting the new one
    /// into the disposer bag.
    public func insert(_ disposable: Disposable) {
        bag = DisposeBag()
        bag?.insert(disposable)
    }
    
    deinit {
        dispose()
    }
}