Kotlin

Kotlin is JetBrains' concise, null-safe language for Android, backend, multiplatform, and serverless workloads.

Keywords

• as, as?, break, class, companion, const, constructor, continue, crossinline
• data, do, else, enum, expect, external
• false, final, finally, for, fun
• if, import, in, infix, init, inline, inner, interface, internal, is
• lateinit, noinline, null, object, open, operator, out, override
• package, private, protected, public
• reified, return, sealed, super, suspend
• this, throw, true, try, typealias, typeof
• val, var, vararg, when, where, while

Language Features

• Null safety via nullable types (`String?`) and Elvis operator `?:`.
• Extension functions/properties add APIs without inheritance.
• Coroutines deliver structured concurrency with `suspend` functions and flows.
• Data classes auto-generate equals/hashCode/toString/copy.
• Sealed classes and `when` expressions model state machines.
• Kotlin Multiplatform shares business logic across JVM, JS, Native.

Standard Library & Ecosystem

• kotlin.collections adds sequence, list, set, map helpers.
• kotlinx.coroutines for flows, actors, channels, structured scopes.
• Android: Jetpack Compose, Ktor client/server, Retrofit, Room.
• Ktor, Spring Boot, Micronaut, and Vert.x support Kotlin-first backends.

Operators & Idioms

• Safe call `?.`, let/apply/run/scope functions, operator overloading (`operator fun plus`).
• Ranges `1..10`, `downTo`, `until`, `step`.
• Destructuring declarations `(val (name, age) = person)`.
• Smart casts automatically narrow types after checks.

Best Practices

• Enable explicit API mode for libraries.
• Favor immutable `val` over `var`.
• Keep coroutine scopes tied to lifecycles (ViewModelScope, lifecycleScope).
• Use `sealed interface` plus `when` with exhaustiveness checks.
• Adopt detekt/kotlinter and run `./gradlew ktlintCheck` in CI.

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