     ///
     /// - Parameter handler: A closure which is invoked when the cache clearing operation finishes.
     ///                      This `handler` will be called from the main queue.
-    open func clearDiskCache(completion handler: (()->())? = nil) {
+    open func clearDiskCache(completion handler: (() -> Void)? = nil) {
         ioQueue.async {
             do {
                 try self.diskStorage.removeAll()

                DispatchQueue.main.async { handler() }
            }
        }
    }

    /// Clears the expired images from disk storage. This is an async operation.

    }

    // MARK: Cleaning
    /// Clears the memory & disk storage of this cache. This is an async operation.
    ///
    /// - Parameter handler: A closure which is invoked when the cache clearing operation finishes.
    ///                      This `handler` will be called from the main queue.
    public func clearCache(completion handler: (() -> Void)? = nil) {
        clearMemoryCache()
        clearDiskCache(completion: handler)
    }
    
    /// Clears the memory storage of this cache.
    @objc public func clearMemoryCache() {
        try? memoryStorage.removeAll()
