Quick Answer

Lightweight threads for non-blocking operations

Understanding the Issue

Kotlin coroutines simplify asynchronous programming by allowing sequential-looking code that executes asynchronously. They are lightweight compared to threads and can suspend execution without blocking threads.

The Problem

This code demonstrates the issue:

Kotlin Error 
// Problem: Callback hell
api.fetchUser { user ->
    api.fetchProfile(user) { profile ->
        api.fetchFriends(profile) { friends ->
            // Nested callbacks
        }
    }
}

The Solution

Here's the corrected code:

Kotlin Fixed 
// Solution: Coroutine implementation
suspend fun loadUserData() = coroutineScope {
    val user = async { api.fetchUser() }
    val profile = async { api.fetchProfile(user.await()) }
    val friends = async { api.fetchFriends(profile.await()) }
    UserData(user.await(), profile.await(), friends.await())
}

// Usage:
lifecycleScope.launch {
    val data = loadUserData()
    updateUI(data)
}

Key Takeaways

Use coroutines to write asynchronous code in a sequential style, avoiding callback hell.