PersistenceManager.swift

/// Manager class responsible of retriving data
final class DataManager {
    /// Memory Cache responsible for maintaining data in memory
    var memory = MemoryCache()
    /// Disc Cache responsible for maintaining data in memory
    var disc = DiscCache()
    /// To get value from persistence for a specific key, data is first checked in memory, 
    /// followed by disc. If data isnot found `nil` is returned
    func get(_ key: key) -> Value? {
        if let value =  memory.get(key) { return value }
        else if let value = disc.get(key) { return value }
        else { return nil }
    }
    /// To set value into persistence for a specific key, data is first saved in memory, 
    /// followed by disc.
    func set(_ key: key, _ value: Value) -> Void {
        memory.set(key, value)
        disc.set(key, value)
    }
    
}