Kotlin Patterns

# Kotlin Development Patterns

Idiomatic Kotlin patterns and best practices for building robust, efficient, and maintainable applications.

## When to Use

- Writing new Kotlin code
- Reviewing Kotlin code
- Refactoring existing Kotlin code
- Designing Kotlin modules or libraries
- Configuring Gradle Kotlin DSL builds

## How It Works

This skill enforces idiomatic Kotlin conventions across seven key areas: null safety using the type system and safe-call operators, immutability via `val` and `copy()` on data classes, sealed classes and interfaces for exhaustive type hierarchies, structured concurrency with coroutines and `Flow`, extension functions for adding behaviour without inheritance, type-safe DSL builders using `@DslMarker` and lambda receivers, and Gradle Kotlin DSL for build configuration.

## Examples

**Null safety with Elvis operator:**
```kotlin
fun getUserEmail(userId: String): String {
    val user = userRepository.findById(userId)
    return user?.email ?: "unknown@example.com"
}
```

**Sealed class for exhaustive results:**
```kotlin
sealed class Result<out T> {
    data class Success<T>(val data: T) : Result<T>()
    data class Failure(val error: AppError) : Result<Nothing>()
    data object Loading : Result<Nothing>()
}
```

**Structured concurrency with async/await:**