kotlin

name	kotlin
description	Kotlin language skill covering null safety, coroutines, data classes, extension functions, and KMP. Use when building Kotlin applications.
trigger	kotlin, kt, kotlinx, kotlin coroutines, kotlin flows, ktor, kotlin multiplatform, kotlin compose

kotlin

Core Concepts

• Null Safety: nullable types (T?), safe call (?.), Elvis operator (?:), non-null assertion (!!), smart casts
• Data Classes: auto-generate equals/hashCode/toString/copy/componentN from primary constructor
• Extension Functions: add methods to existing types without inheritance, receiver parameter syntax
• Sealed Classes: restricted class hierarchies, exhaustive when branches, sum type pattern

Coroutines & Flows

• Coroutines: suspend functions, launch/async builders, structured concurrency via scope
• Flows: cold asynchronous streams, terminal operators (collect/toList), intermediate (map/filter)
• Channels: hot streams for producer-consumer, rendezvous/buffered, ticker channels
• Dispatchers: Main (UI), IO (disk/network), Default (CPU), Unconfined (inherited)

Multiplatform & Compose

• KMP: shared business logic across JVM, JS, Native; expect/actual for platform declarations
• Compose Multiplatform: declarative UI framework, @Composable functions, state hoisting
• kotlinx.serialization: @Serializable annotation, JSON/protobuf/CBOR formats, polymorphic serialization
• Build system: Kotlin DSL for Gradle, multiplatform plugin, source set hierarchy