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# Reflection Capabilities
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## Overview
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The Reflection capabilities provide type introspection support for WASI applications. The implementation focuses on compile-time type reflection using Kotlin's reified generics, enabling applications to obtain runtime type information for generic type parameters.
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## API Reference
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### Type Reflection Functions
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```kotlin { .api }
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/**
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 * Returns the runtime representation of the given type T.
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 * Uses compile-time type information to create KType instances.
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 * @return KType representing the type T
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 */
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inline fun <reified T> typeOf(): KType
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/**
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 * Returns the runtime representation of the given type T with lazy initialization.
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 * Optimized version that delays KType creation until first access.
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 * @return KType representing the type T
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 */
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inline fun <reified T> typeOfLazyInit(): KType
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```
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### KType Interface
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```kotlin { .api }
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/**
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 * Represents a type in the Kotlin type system.
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 */
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interface KType {
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    /**
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     * The classifier of this type, typically a KClass.
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     */
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    val classifier: KClassifier?
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    /**
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     * Type arguments for generic types.
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     */
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    val arguments: List<KTypeProjection>
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    /**
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     * Whether this type is marked as nullable.
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     */
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    val isMarkedNullable: Boolean
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}
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```
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## Usage Examples
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### Basic Type Reflection
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```kotlin
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// Get type information for primitive types
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val stringType = typeOf<String>()
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val intType = typeOf<Int>()
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val booleanType = typeOf<Boolean>()
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println("String type: $stringType")
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println("Int type: $intType")
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println("Boolean type: $booleanType")
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// Check type properties
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println("String is nullable: ${stringType.isMarkedNullable}") // false
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println("String classifier: ${stringType.classifier}")
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```
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### Nullable Type Reflection
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```kotlin
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// Compare nullable and non-nullable types
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val nonNullableString = typeOf<String>()
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val nullableString = typeOf<String?>()
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println("Non-nullable: $nonNullableString")
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println("Nullable: $nullableString")
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println("Nullable marked: ${nullableString.isMarkedNullable}") // true
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println("Types equal: ${nonNullableString == nullableString}") // false
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```
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### Generic Type Reflection
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```kotlin
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// Reflect on generic types
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val listOfStrings = typeOf<List<String>>()
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val mapOfStringToInt = typeOf<Map<String, Int>>()
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val setOfNullableInts = typeOf<Set<Int?>>()
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println("List<String>: $listOfStrings")
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println("Map<String, Int>: $mapOfStringToInt")
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println("Set<Int?>: $setOfNullableInts")
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// Access type arguments
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val listArgs = listOfStrings.arguments
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println("List type arguments: $listArgs")
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if (listArgs.isNotEmpty()) {
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    val elementType = listArgs[0].type
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    println("List element type: $elementType")
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}
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```
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### Collection Type Analysis
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```kotlin
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// Analyze collection types
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fun analyzeCollectionType(type: KType) {
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    when (type.classifier) {
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        List::class -> {
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            println("This is a List type")
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            val elementType = type.arguments.firstOrNull()?.type
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            println("Element type: $elementType")
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        }
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        Set::class -> {
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            println("This is a Set type")
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            val elementType = type.arguments.firstOrNull()?.type
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            println("Element type: $elementType")
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        }
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        Map::class -> {
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            println("This is a Map type")
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            val keyType = type.arguments.getOrNull(0)?.type
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            val valueType = type.arguments.getOrNull(1)?.type
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            println("Key type: $keyType")
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            println("Value type: $valueType")
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        }
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        else -> {
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            println("Unknown collection type: ${type.classifier}")
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        }
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    }
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}
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// Usage
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analyzeCollectionType(typeOf<List<String>>())
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analyzeCollectionType(typeOf<Map<String, Int>>())
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analyzeCollectionType(typeOf<Set<Double>>())
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```
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### Type-Safe Configuration
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```kotlin
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// Type-safe configuration system using reflection
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class ConfigurationManager {
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    private val values = mutableMapOf<KType, Any?>()
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    inline fun <reified T> set(value: T) {
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        values[typeOf<T>()] = value
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    }
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    inline fun <reified T> get(): T? {
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        @Suppress("UNCHECKED_CAST")
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        return values[typeOf<T>()] as? T
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    }
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    inline fun <reified T> getOrDefault(defaultValue: T): T {
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        return get<T>() ?: defaultValue
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    }
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    inline fun <reified T> has(): Boolean {
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        return typeOf<T>() in values
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    }
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}
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// Usage
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val config = ConfigurationManager()
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config.set("localhost")
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config.set(8080)
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config.set(true)
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val host: String? = config.get<String>()
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val port: Int = config.getOrDefault(3000)
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val debug: Boolean = config.getOrDefault(false)
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println("Host: $host")
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println("Port: $port")
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println("Debug: $debug")
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```
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### Serialization Support
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```kotlin
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// Type-aware serialization helper
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object TypedSerializer {
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    private val serializers = mutableMapOf<KType, (Any?) -> String>()
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    private val deserializers = mutableMapOf<KType, (String) -> Any?>()
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    inline fun <reified T> registerSerializer(
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        noinline serializer: (T?) -> String,
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        noinline deserializer: (String) -> T?
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    ) {
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        val type = typeOf<T>()
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        @Suppress("UNCHECKED_CAST")
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        serializers[type] = serializer as (Any?) -> String
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        @Suppress("UNCHECKED_CAST")
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        deserializers[type] = deserializer as (String) -> Any?
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    }
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    inline fun <reified T> serialize(value: T?): String? {
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        val type = typeOf<T>()
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        return serializers[type]?.invoke(value)
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    }
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    inline fun <reified T> deserialize(data: String): T? {
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        val type = typeOf<T>()
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        @Suppress("UNCHECKED_CAST")
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        return deserializers[type]?.invoke(data) as? T
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    }
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}
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// Register serializers
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TypedSerializer.registerSerializer<String>(
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    { it ?: "null" },
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    { if (it == "null") null else it }
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)
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TypedSerializer.registerSerializer<Int>(
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    { it?.toString() ?: "null" },
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    { if (it == "null") null else it.toIntOrNull() }
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)
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// Use type-safe serialization
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val serialized = TypedSerializer.serialize("Hello")
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val deserialized: String? = TypedSerializer.deserialize(serialized ?: "")
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println("Serialized: $serialized")
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println("Deserialized: $deserialized")
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```
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### Generic Function Utilities
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```kotlin
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// Type-safe generic utilities
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object TypeUtils {
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    inline fun <reified T> typeName(): String {
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        return typeOf<T>().toString()
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    }
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    inline fun <reified T> isNullable(): Boolean {
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        return typeOf<T>().isMarkedNullable
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    }
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    inline fun <reified T> isList(): Boolean {
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        return typeOf<T>().classifier == List::class
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    }
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    inline fun <reified T> isMap(): Boolean {
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        return typeOf<T>().classifier == Map::class
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    }
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    inline fun <reified Collection> getElementType(): KType? {
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        val type = typeOf<Collection>()
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        return type.arguments.firstOrNull()?.type
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    }
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}
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// Usage examples
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println("String name: ${TypeUtils.typeName<String>()}")
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println("String? nullable: ${TypeUtils.isNullable<String?>()}")
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println("List<Int> is list: ${TypeUtils.isList<List<Int>>()}")
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println("Map<String, Int> is map: ${TypeUtils.isMap<Map<String, Int>>()}")
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val elementType = TypeUtils.getElementType<List<String>>()
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println("List<String> element type: $elementType")
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```
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### Lazy Type Initialization
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```kotlin
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// Use lazy type initialization for performance
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class TypeRegistry {
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    private val lazyTypes = mutableMapOf<String, Lazy<KType>>()
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    inline fun <reified T> registerLazy(name: String) {
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        lazyTypes[name] = lazy { typeOfLazyInit<T>() }
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    }
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    fun getType(name: String): KType? {
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        return lazyTypes[name]?.value
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    }
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    fun hasType(name: String): Boolean {
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        return name in lazyTypes
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    }
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}
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// Register types lazily
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val registry = TypeRegistry()
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registry.registerLazy<String>("string")
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registry.registerLazy<List<Int>>("intList")
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registry.registerLazy<Map<String, Any?>>("stringMap")
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// Access types only when needed
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val stringType = registry.getType("string")
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println("Retrieved string type: $stringType")
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```
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## Implementation Details
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### Compile-Time Type Resolution
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The WASI reflection implementation uses compile-time type resolution:
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- **Reified Generics**: Type parameters are resolved at compile time
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- **No Runtime Class Loading**: No dynamic class loading or bytecode analysis
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- **Static Type Information**: All type information is embedded at compile time
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### Memory Efficiency
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- **Lazy Initialization**: `typeOfLazyInit` delays KType creation until first access
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- **Type Caching**: Identical types may be cached to reduce memory usage
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- **Minimal Overhead**: No heavy reflection infrastructure in WASI environment
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### Limitations
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#### No Runtime Class Analysis
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```kotlin
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// NOT SUPPORTED: Runtime class introspection
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// val methods = SomeClass::class.members // Not available
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// val properties = SomeClass::class.memberProperties // Not available
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// SUPPORTED: Compile-time type information only
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val type = typeOf<SomeClass>()
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val classifier = type.classifier
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```
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#### No Dynamic Method Invocation
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```kotlin
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// NOT SUPPORTED: Dynamic method calls
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// val method = SomeClass::class.functions.find { it.name == "someMethod" }
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// method?.call(instance, args) // Not available
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// SUPPORTED: Static type checking only
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fun processType(type: KType) {
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    when (type.classifier) {
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        String::class -> println("Processing string type")
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        Int::class -> println("Processing int type")
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    }
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}
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```
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## Performance Considerations
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### Type Comparison Performance
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```kotlin
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// Type comparison is efficient
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val type1 = typeOf<String>()
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val type2 = typeOf<String>()
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val equal = type1 == type2 // Fast comparison
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// Cache types for repeated use
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class TypeCache {
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    private val stringType = typeOf<String>()
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    private val intType = typeOf<Int>()
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    fun isString(type: KType) = type == stringType
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    fun isInt(type: KType) = type == intType
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}
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```
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### Lazy Initialization Benefits
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```kotlin
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// Use lazy initialization for large type hierarchies
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object SchemaTypes {
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    val userType by lazy { typeOfLazyInit<User>() }
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    val productType by lazy { typeOfLazyInit<Product>() }
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    val orderType by lazy { typeOfLazyInit<Order>() }
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    // Types are only created when first accessed
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}
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```
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## Best Practices
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### Type Safety
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```kotlin
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// DO: Use reified generics for type safety
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inline fun <reified T> processTypedValue(value: Any?): T? {
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    val expectedType = typeOf<T>()
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    // Use type information for safe casting
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    return value as? T
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}
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// DON'T: Rely on runtime class checking (not available)
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// fun processValue(value: Any, clazz: Class<*>) // Not supported in WASI
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```
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### Performance Optimization
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```kotlin
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// DO: Cache frequently used types
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object CommonTypes {
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    val STRING = typeOf<String>()
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    val INT = typeOf<Int>()
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    val BOOLEAN = typeOf<Boolean>()
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}
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// DO: Use lazy initialization for expensive type hierarchies
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val complexType by lazy { typeOfLazyInit<ComplexGenericType<List<Map<String, Any?>>>>() }
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// AVOID: Repeated type creation in hot paths
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// Bad:
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repeat(1000) {
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    val type = typeOf<String>() // Creates type object each time
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}
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// Better:
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val cachedType = typeOf<String>()
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repeat(1000) {
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    // Use cachedType
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}
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```
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### Type Registry Pattern
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```kotlin
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// Recommended pattern for managing multiple types
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class ApplicationTypes {
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    companion object {
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        private val types = mapOf(
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            "user" to typeOf<User>(),
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            "product" to typeOf<Product>(),
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            "order" to typeOf<Order>()
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        )
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        fun getType(name: String): KType? = types[name]
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        fun hasType(name: String): Boolean = name in types
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    }
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}
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```