autojanet/skills/understand/languages/kotlin.md

Kotlin Language Prompt Snippet

Key Concepts

• Coroutines and Flow: Structured concurrency with suspending functions; Flow for reactive streams
• Data Classes: Auto-generated equals, hashCode, toString, copy, and destructuring
• Sealed Classes/Interfaces: Restricted hierarchies enabling exhaustive when expressions
• Extension Functions: Add methods to existing classes without inheritance or wrappers
• Null Safety: ?. safe call, !! non-null assertion, ?: Elvis operator for default values
• Delegation (by keyword): Delegate interface implementation or property access to another object
• DSL Builders: Lambda-with-receiver syntax enabling type-safe builder patterns
• Inline Functions and Reified Types: Inline for zero-overhead lambdas; reified for runtime type access
• Companion Objects: Named or anonymous singleton associated with a class (replaces static members)
• Scope Functions: let, run, apply, also, with for concise object configuration and transformation

Import Patterns

• import package.ClassName — import a specific class
• import package.* — wildcard import of all declarations in a package
• import package.function as alias — import with alias to resolve naming conflicts

File Patterns

• build.gradle.kts — Gradle build script using Kotlin DSL
• Application.kt — application entry point (Spring Boot or Ktor)
• src/main/kotlin/ — main source root following Gradle conventions
• src/test/kotlin/ — test source root with matching package structure
• settings.gradle.kts — multi-module project configuration

Common Frameworks

• Spring Boot (Kotlin) — Kotlin-first support with coroutines and DSL extensions
• Ktor — Kotlin-native async web framework from JetBrains
• Jetpack Compose — Declarative UI toolkit for Android using composable functions
• Exposed — Lightweight SQL framework with type-safe DSL and DAO patterns
• Koin — Pragmatic dependency injection framework using Kotlin DSL

Example Language Notes

Uses sealed class hierarchy with when exhaustive matching to handle all possible API response states. The compiler enforces that every variant is covered, eliminating the need for a fallback else branch and catching missing cases at compile time.

Extension functions allow adding utilities like String.toSlug() without modifying the original class — keeping the extension discoverable through IDE auto-complete.