ComputesVersusStoredExplained.swift

//: Playground - noun: a place where people can play

import UIKit

// Computed property
// NOTE: Since a computed property gets reassigned upon every access!, it can only be declared as a var and not a let.
var urlSession: URLSession {
    let urlSessionConfiguration: URLSessionConfiguration = URLSessionConfiguration.default.copy() as! URLSessionConfiguration
    urlSessionConfiguration.requestCachePolicy = NSURLRequest.CachePolicy.returnCacheDataElseLoad
    
    // some further configuration
    
    return URLSession(configuration: urlSessionConfiguration)
}


// Stored property
// Stored properties get initialized once
// This is made clear by the fact that this is actually an assignment operation (denoted by the = operator) and that the closure gets executed prior to the assignment,(The () brackets after the closure).
let urlSession1: URLSession = {
    let urlSessionConfiguration: URLSessionConfiguration = URLSessionConfiguration.default.copy() as! URLSessionConfiguration
    urlSessionConfiguration.requestCachePolicy = NSURLRequest.CachePolicy.returnCacheDataElseLoad
    
    // some further configuration
    
    return URLSession(configuration: urlSessionConfiguration)
}()

for _ in 1...10 {
    print(urlSession1
    )
}