Kotlin

Kotlin Skill Architecture

1. Skill Context

Focus: Android development, Modern JVM Backend (Spring Boot), Multiplatform (KMP), null safety, coroutines. Triggers: kotlin, k8s, spring boot, android, jvm, coroutines, null-safety.

2. Core Principles

• 100% Java Interoperability: Kotlin compiles to JVM bytecode. You can call Java from Kotlin and vice versa seamlessly.
• Null Safety by Default: The type system distinguishes between nullable (String?) and non-nullable (String) types, effectively eliminating NullPointerException (The Billion Dollar Mistake).
• Extension Functions: You can add new methods to existing classes (even final ones like String) without inheriting from them.

3. Anti-Patterns

• The !! Operator: Force-unwrapping a nullable type. If it's null, it throws an NPE. Only use this if you mathematically prove to the compiler something cannot be null, but prefer ?: (Elvis operator).
• Global Mutable State in Coroutines: Coroutines run on multiple threads. Mutating a shared variable without Mutex or Atomic types causes race conditions.
• Heavy computations in Dispatchers.Main: Blocking the main thread in Android freezes the UI. Always switch to Dispatchers.Default for CPU work and Dispatchers.IO for network/DB work.

4. References

• references/kotlin-fundamentals.md — Nullability, Data Classes, Scope Functions.
• references/kotlin-advanced.md — Coroutines, Flows, Inline Classes.
• references/kotlin-testing.md — MockK, Kotest, Coroutine Testing.