Kotlin Const Property

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Declaration Requirements

1. Placement: It must be declared at the top level of a file, as a member of an object declaration, or within a companion object. It cannot be a standard class property or a local variable.
2. Type Restriction: The property type must be a String or a primitive type (Int, Long, Double, Float, Boolean, Char, Byte, Short).
3. Initialization: It must be initialized immediately with a literal value or another compile-time constant. It cannot be initialized by a function call that requires runtime execution.
4. No Custom Getters: It cannot have a custom getter implementation, as the value must be statically determinable at compile time.

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Syntax

// 1. Top-level declaration with visibility modifiers
private const val MAX_CONNECTIONS: Int = 10
const val DEPRECATION_REASON: String = "Use V2 API instead"

// Annotation argument capability (invalid with standard 'val')
@Deprecated(DEPRECATION_REASON)
fun legacyFunction() {}

class DatabaseClient {
    // 2. Companion object declaration
    companion object {
        internal const val TIMEOUT_MS: Long = 5000L
    }
}

// 3. Object declaration (Singleton)
object AppConfig {
    const val VERSION_CODE: Int = 1
}

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Compilation Behavior and Bytecode

val runtimeConstant = 100

public const val COMPILE_CONSTANT = 100

val total = COMPILE_CONSTANT + 50

// Equivalent Java bytecode representation
int total = 150;