Summary

# Kotlin summary

You can now:

- Write idiomatic Kotlin - data classes, sealed classes, when expressions
- Use null safety: ? !! ?: let
- Reach for extension functions to make APIs read naturally
- Work with collections: map, filter, fold, sequence
- Build coroutines with suspend, launch, async, withContext, and Flow
- Understand Android lifecycle hooks and ViewModel + StateFlow
- Write multi-module Gradle builds with the Kotlin DSL
- Use Ktor or Spring Boot for server-side Kotlin

# Your next step - Flow + StateFlow

import kotlinx.coroutines.flow.*
import kotlinx.coroutines.*

data class User(val id: Int, val name: String)

class UserViewModel {
    private val _users = MutableStateFlow<List<User>>(emptyList())
    val users: StateFlow<List<User>> = _users.asStateFlow()

    suspend fun load() {
        _users.value = fetch()
    }

    private suspend fun fetch(): List<User> = withContext(Dispatchers.IO) {
        delay(200) // mock API
        listOf(User(1, 'Ada'), User(2, 'Linus'))
    }
}

// Next: KMP (Kotlin Multiplatform), Compose Multiplatform, Coroutines Flow deep dive.