Moai Lang Kotlin

Lang Kotlin Skill - Enterprise v4.0.0

Skill Overview

Kotlin 2.0 Multiplatform enterprise development with advanced async patterns, KMP architecture, and Compose Multiplatform UI. This skill provides patterns for mobile, backend, and cross-platform development with full Context7 MCP integration for real-time documentation access.

Core Capabilities

• ✅ Kotlin 2.0 Multiplatform (KMP) enterprise architecture
• ✅ Advanced coroutines and structured concurrency patterns
• ✅ Compose Multiplatform UI development (Android, iOS, Web)
• ✅ Enterprise testing strategies with Kotest and MockK
• ✅ Context7 MCP integration for latest documentation
• ✅ Performance optimization and memory management
• ✅ Modern architecture patterns (MVI, Clean Architecture)
• ✅ Security best practices for production systems

Quick Reference

When to Use This Skill

Automatic activation:

• Kotlin/KMP development discussions
• Multiplatform project architecture and design
• Mobile development with shared business logic
• Async programming and coroutine patterns
• Compose Multiplatform UI development

Manual invocation:

• Design multiplatform architecture
• Implement advanced async patterns
• Optimize performance and memory usage
• Review enterprise Kotlin code

Technology Stack (2025-11-13)

Core Language Features

1. Null Safety & Type System

Kotlin's null safety is a game-changer for enterprise development:

// Smart null handling
val name: String? = "John"
val length = name?.length ?: 0  // Safe navigation + Elvis operator

// Type-safe IDs with inline classes
@JvmInline
value class UserId(val value: String)

// Sealed hierarchies for domain modeling
sealed class Result<T> {
    data class Success<T>(val data: T) : Result<T>()
    data class Error(val exception: Throwable) : Result<Nothing>()
}

Key Benefits:

• Eliminates NullPointerException at compile time
• Zero runtime overhead with inline classes
• Type-safe domain models

2. Coroutines - Structured Concurrency

Enterprise async patterns with built-in safety:

// Structured concurrency scope
coroutineScope {
    val result1 = async { fetchData("API1") }
    val result2 = async { fetchData("API2") }
    awaitAll(result1, result2)
} // All coroutines cancelled if scope exits

// Context switching
withContext(Dispatchers.IO) {
    val data = blockingIoCall()  // Safe switching
}

// Error isolation with supervisor scope
supervisorScope {
    launch { riskyOperation1() }  // Failure doesn't affect others
    launch { riskyOperation2() }
}

Key Benefits:

• Automatic cancellation and resource cleanup
• Prevents memory leaks and zombie coroutines
• Context-aware execution

3. Extension Functions & DSLs

Powerful language extension without inheritance:

// Domain-specific languages (DSLs)
fun html(block: HtmlBuilder.() -> Unit): String {
    val builder = HtmlBuilder()
    builder.block()
    return builder.build()
}

// Usage
val page = html {
    h1("Welcome")
    p("This is a paragraph")
}

// See examples.md for complete DSL patterns

Multiplatform Architecture

Project Structure

kmp-enterprise-app/
├── shared/
│   ├── src/
│   │   ├── commonMain/kotlin/
│   │   │   ├── domain/        # Business logic
│   │   │   ├── data/          # Data layer
│   │   │   └── presentation/  # State management
│   │   ├── androidMain/kotlin/
│   │   ├── iosMain/kotlin/
│   │   └── commonTest/kotlin/
├── androidApp/
├── iosApp/
└── webApp/

expect/actual Pattern

// commonMain: Define interface
expect class PlatformDatabase {
    suspend fun saveData(data: String): Result<Unit>
}

// androidMain: Android implementation
actual class PlatformDatabase {
    actual suspend fun saveData(data: String) = try {
        room.insert(data)
        Result.success(Unit)
    } catch (e: Exception) {
        Result.failure(e)
    }
}

// iosMain: iOS implementation
actual class PlatformDatabase {
    actual suspend fun saveData(data: String) = try {
        coreData.save(data)
        Result.success(Unit)
    } catch (e: Exception) {
        Result.failure(e)
    }
}

Key Pattern:

• Share business logic in commonMain
• Isolate platform specifics in platform modules
• Compile-time platform selection

Advanced Async Patterns

Flow - Reactive Streams

// Create cold flow (lazy)
fun getUsersFlow(): Flow<User> = flow {
    while (true) {
        val users = repository.fetchUsers()
        emit(users)
        delay(5000)  // Refresh every 5 seconds
    }
}

// Compose flows
getUsersFlow()
    .map { it.copy(name = it.name.uppercase()) }
    .filter { it.isActive }
    .distinctUntilChanged()
    .collect { updateUI(it) }

StateFlow - Mutable State

class CounterViewModel {
    private val _count = MutableStateFlow(0)
    val count: StateFlow<Int> = _count.asStateFlow()

    fun increment() { _count.value++ }
    fun decrement() { _count.value-- }
}

// Observe state changes
viewModel.count.collect { count ->
    updateUI("Count: $count")
}

Compose Multiplatform UI

Basic Components

@Composable
fun UserListScreen(users: List<User>) {
    Column(modifier = Modifier.fillMaxSize()) {
        Text("Users", style = MaterialTheme.typography.headlineLarge)

        LazyColumn {
            items(users) { user ->
                UserCard(user)
            }
        }
    }
}

@Composable
fun UserCard(user: User) {
    Card(modifier = Modifier.fillMaxWidth().padding(8.dp)) {
        Column(modifier = Modifier.padding(16.dp)) {
            Text(user.name, style = MaterialTheme.typography.titleMedium)
            Text(user.email, color = Color.Gray)
        }
    }
}

Key Concepts:

• Declarative UI
• Reusable components
• State management integration

Enterprise Patterns

Dependency Injection with Koin

val appModule = module {
    single { HttpClient() }
    single { UserRepository(get()) }
    viewModel { UserListViewModel(get()) }
}

// Usage
val userService: UserService = get()  // Injected automatically

Error Handling

// Result wrapper for safe operations
suspend fun fetchData(): Result<String> = try {
    Result.success(apiCall())
} catch (e: Exception) {
    Result.failure(e)
}

// Chain operations safely
fetchData()
    .onSuccess { data -> updateUI(data) }
    .onFailure { error -> showError(error) }

Testing

@Test
fun testAsync() = runTest {
    val result = someAsyncFunction()
    assertEquals("expected", result)
}

@Test
fun testWithMock() {
    val repo = mockk<Repository>()
    coEvery { repo.fetch("1") } returns "data"
    // Verify behavior
    coVerify { repo.fetch("1") }
}

Context7 MCP Integration

This skill integrates with Context7 for real-time access to official documentation:

Available Resources

1. Kotlin Language: /kotlin/kotlin
2. Coroutines: /kotlin/kotlinx.coroutines
3. KMP: /kotlin/kotlin.multiplatform
4. Compose: /jetbrains/compose-multiplatform
5. Ktor: /ktor/ktor
6. Serialization: /kotlin/kotlinx.serialization

Usage Example

// Get latest coroutine patterns
val docs = mcp__context7__get-library-docs(
    context7CompatibleLibraryID = "/kotlin/kotlinx.coroutines"
)

Performance Optimization

Memory Efficiency

1. Use Sequence for lazy evaluation:

   (1..1_000_000).asSequence()
       .filter { it % 2 == 0 }
       .map { it * 2 }
       .toList()  // Only processes what's needed
   

2. Inline classes for zero-overhead:

   @JvmInline
   value class UserId(val value: String)  // No allocation at runtime
   

3. Primitive arrays instead of boxed:

   val intArray = IntArray(1000)  // More efficient than Array<Int>
   

Execution Speed

1. Tail recursion:

   tailrec fun factorial(n: Int, acc: Int = 1): Int =
       if (n <= 1) acc else factorial(n - 1, n * acc)
   

2. Coroutine pooling (automatic with structured concurrency)

Best Practices

1. Always Use Structured Concurrency

// GOOD
coroutineScope {
    val result = async { fetchData() }
}

// AVOID
GlobalScope.launch { fetchData() }  // Never use

2. Null Safety Over Exceptions

// GOOD
val user = repository.findUser(id)
    ?.let { updateUI(it) }
    ?: showNotFound()

// AVOID
val user = repository.findUser(id)!!  // Unsafe

3. Resource Management

// GOOD
File("data.txt").bufferedReader().use { reader ->
    reader.readLines()
}  // Auto-closes

// GOOD
try {
    // Use resource
} finally {
    resource.close()
}

Security Considerations

Input Validation

data class SecureUserInput(val email: String) {
    init {
        require(email.contains("@")) { "Invalid email" }
        require(email.length <= 254) { "Email too long" }
    }
}

Secure Storage

expect class SecureStorage {
    suspend fun store(key: String, value: String)
    suspend fun retrieve(key: String): String?
}

Network Security

// Certificate pinning
val client = HttpClient {
    install(Auth) {
        bearer {
            loadTokens { getBearerTokens() }
        }
    }
}

Testing Strategy

Works Well With

• moai-foundation-trust (TRUST 5 quality gates)
• moai-foundation-security (Enterprise security)
• moai-foundation-testing (Testing strategies)
• moai-cc-mcp-integration (MCP integration)
• moai-essentials-debug (Debugging)

For Complete Information

• Working Examples: See examples.md (29 examples covering all patterns)
• CLI Reference: See reference.md (installation, commands, troubleshooting)
• Official Docs: https://kotlinlang.org
• Coroutines Guide: https://kotlinlang.org/docs/coroutines-overview.html

Changelog

• v4.0.0 (2025-11-13): Refactored to Progressive Disclosure with comprehensive examples.md and reference.md
• v3.0.0 (2025-03-15): Added KMP and multiplatform patterns
• v2.0.0 (2025-01-10): Basic Kotlin patterns and best practices
• v1.0.0 (2024-12-01): Initial release

Last updated: 2025-11-13