// Inline function — eliminates lambda allocation overhead inline fun measureTime(block: () -> T): Pair { val start = System.nanoTime() val result = block() // Inlined at call site, no lambda object created val duration = (System.nanoTime() - start) / 1_000_000 return result to duration } // Reified — type parameter available at runtime inline fun Intent.getParcelableExtraCompat(key: String): T? { return if (Build.VERSION.SDK_INT >= 33) { getParcelableExtra(key, T::class.java) } else { @Suppress("DEPRECATION") getParcelableExtra(key) as? T } } // Usage: val user = intent.getParcelableExtraCompat("user") // Without reified, you'd need to pass Class explicitly // DSL Building — type-safe builders @DslMarker annotation class NetworkDsl @NetworkDsl class RequestBuilder { var url: String = "" var method: String = "GET" private val headers = mutableMapOf() private var body: String? = null fun headers(block: HeaderBuilder.() -> Unit) { HeaderBuilder(headers).apply(block) } fun body(content: String) { body = content } fun build() = Request(url, method, headers, body) } @NetworkDsl class HeaderBuilder(private val headers: MutableMap) { infix fun String.to(value: String) { headers[this] = value } } fun request(block: RequestBuilder.() -> Unit): Request { return RequestBuilder().apply(block).build() } // Usage — reads like natural language val req = request { url = "https://api.example.com/users" method = "POST" headers { "Authorization" to "Bearer token123" "Content-Type" to "application/json" } body("""{"name": "Alice"}""") } // Sealed interface — exhaustive state modeling sealed interface NetworkState { data object Idle : NetworkState data object Loading : NetworkState data class Success(val data: T) : NetworkState sealed interface Error : NetworkState { data class Network(val message: String) : Error data class Server(val code: Int, val message: String) : Error data class Auth(val reason: String) : Error } } // Exhaustive when — compiler ensures all cases handled fun handleState(state: NetworkState) = when (state) { is NetworkState.Idle -> showIdle() is NetworkState.Loading -> showSpinner() is NetworkState.Success -> showData(state.data) is NetworkState.Error.Network -> showRetry(state.message) is NetworkState.Error.Server -> showServerError(state.code) is NetworkState.Error.Auth -> navigateToLogin() // No 'else' needed — compiler verifies exhaustiveness } // Value class — zero overhead type safety @JvmInline value class UserId(val value: String) @JvmInline value class Email(val value: String) { init { require(value.contains("@")) { "Invalid email" } } } fun getUser(id: UserId): User { /* ... */ } // getUser(UserId("123")) ← clear intent // getUser("123") ← compile error! Type safety without runtime cost

Phase 4: Kotlin Mastery (Senior Level)

Coroutines Internals & CPS Transformation

Structured Concurrency

Flow: Cold vs Hot Streams

Exception & Cancellation Handling in Coroutines

Advanced Kotlin: Inline, Reified, DSLs & Sealed Types

🎤 Mock Interview