Is it possible to implement the main execution loop in the application, and how to do it?

In iOS applications, the main run loop is implemented by the system and managed by the UIKit or SwiftUI framework. However, if you need to create your own loop, for example, to handle events or timers, you can use the RunLoop class.

Example of creating and running your own loop:

let runLoop = RunLoop.current
let distantFuture = Date.distantFuture

// Add an event source, such as a timer
let timer = Timer(timeInterval: 1.0, repeats: true) { _ in
    print("Timer triggered")
}
runLoop.add(timer, forMode: .default)

// Run the loop manually
while runLoop.run(mode: .default, before: distantFuture) {
    // The loop will run as long as the condition is true
}

However, in most cases in iOS development, it is not necessary to implement the main loop yourself, as the system manages it by calling application lifecycle methods and handling events.