Advanced Features and Best Practices in Kotlin

Advanced Features and Best Practices in Kotlin

Let’s dive into some advanced Kotlin features and best practices that will help you write more efficient, maintainable, and idiomatic Kotlin code.

Type-Safe Builders

DSL Creation

class HTML {
    fun body(init: Body.() -> Unit) {
        val body = Body()
        body.init()
    }
}

class Body {
    fun div(init: Div.() -> Unit) {
        val div = Div()
        div.init()
    }
}

class Div {
    var text: String = ""
}

fun html(init: HTML.() -> Unit): HTML {
    val html = HTML()
    html.init()
    return html
}

// Usage
val htmlContent = html {
    body {
        div {
            text = "Hello, Kotlin!"
        }
    }
}

Inline Functions

Basic Inline

inline fun measureTime(action: () -> Unit): Long {
    val startTime = System.currentTimeMillis()
    action()
    return System.currentTimeMillis() - startTime
}

// Usage
val time = measureTime {
    // Code to measure
}

Crossinline and Noinline

inline fun processItems(
    items: List<Int>,
    crossinline onItem: (Int) -> Unit,
    noinline onComplete: () -> Unit
) {
    items.forEach { item ->
        onItem(item)
    }
    onComplete()
}

Reified Type Parameters

Type-Safe Functions

inline fun <reified T> createInstance(): T {
    return T::class.java.getDeclaredConstructor().newInstance()
}

// Usage
val string = createInstance<String>()

Type Checking

inline fun <reified T> List<*>.filterIsInstance(): List<T> {
    return filter { it is T }.map { it as T }
}

// Usage
val strings: List<String> = listOf(1, "2", 3).filterIsInstance()

Delegated Properties

Lazy Initialization

class ExpensiveResource {
    val data by lazy {
        // Expensive computation
        computeData()
    }
}

Observable Properties

class User {
    var name: String by Delegates.observable("") {
        prop, old, new ->
        println("$old -> $new")
    }
}

Vetoable Properties

class PositiveNumber {
    var value: Int by Delegates.vetoable(0) {
        prop, old, new ->
        new > 0
    }
}

Scope Functions

Let

val result = nullableValue?.let {
    // Safe call on non-null value
    it.process()
}

With

val result = with(object) {
    // Multiple operations on the same object
    property1 = value1
    property2 = value2
    computeResult()
}

Apply

val result = object.apply {
    // Configure object
    property1 = value1
    property2 = value2
}

Advanced Coroutines

Structured Concurrency

suspend fun fetchData() = coroutineScope {
    val users = async { fetchUsers() }
    val posts = async { fetchPosts() }

    Data(users.await(), posts.await())
}

Supervisor Scope

supervisorScope {
    val first = async { fetchFirst() }
    val second = async { fetchSecond() }

    try {
        val result = first.await() + second.await()
    } catch (e: Exception) {
        // Handle error
    }
}

Best Practices

Null Safety

// Good
val length = nullableString?.length ?: 0

// Avoid
val length = if (nullableString != null) nullableString.length else 0

Immutability

// Good
val immutableList = listOf(1, 2, 3)

// Avoid
val mutableList = mutableListOf(1, 2, 3)

Function Types

// Good
typealias Handler = (String) -> Unit

// Avoid
fun handleString(string: String) { /* ... */ }

Performance Optimization

Sequence Usage

// Good for large collections
val result = list.asSequence()
    .filter { it > 0 }
    .map { it * 2 }
    .toList()

// Avoid for small collections
val result = list
    .filter { it > 0 }
    .map { it * 2 }

Memory Management

// Good
class Resource : AutoCloseable {
    override fun close() {
        // Cleanup
    }
}

// Usage
Resource().use { resource ->
    // Use resource
}

Testing Best Practices

Property-Based Testing

@Test
fun testAddition() {
    forAll { a: Int, b: Int ->
        (a + b) == (b + a)
    }
}

Coroutine Testing

@Test
fun testCoroutine() = runTest {
    val result = async { computeValue() }.await()
    assertEquals(expected, result)
}

Conclusion

Advanced Kotlin features help you:

• Write more concise and expressive code
• Improve code safety and reliability
• Optimize performance
• Follow best practices

Remember:

• Use appropriate scope functions
• Leverage type-safe builders
• Follow Kotlin idioms
• Write testable code

Stay tuned for more Kotlin programming tips and tricks!