kotlin.util.Lazy.kt Maven / Gradle / Ivy
@file:kotlin.jvm.JvmName("LazyKt")
package kotlin
import java.io.Serializable
/**
* Represents a value with lazy initialization.
*
* To create an instance of [Lazy] use the [lazy] function.
*/
public abstract class Lazy internal constructor() {
/** Gets the lazily initialized value of the current Lazy instance. */
public abstract val value: T
/** Returns `true` if a value for this Lazy instance has been already initialized, and `false` otherwise.
* Once this function has returned `true` it stays `true` for the rest of lifetime of this Lazy instance.
*/
public abstract fun isInitialized(): Boolean
}
/**
* Creates a new instance of the [Lazy] that is already initialized with the specified [value].
*/
public fun lazyOf(value: T): Lazy = InitializedLazyImpl(value)
/* Not available on platform: JS */
/* Not available on platform: JS */
/* Not available on platform: JS */
/**
* An extension to delegate a read-only property of type [T] to an instance of [Lazy].
*
* This extension allows to use instances of Lazy for property delegation:
* `val property: String by lazy { initializer }`
*/
public fun Lazy.get(thisRef: Any?, property: PropertyMetadata): T = value
/**
* Specifies how a [Lazy] instance synchronizes access among multiple threads.
*/
public enum class LazyThreadSafetyMode {
/**
* Locks are used to ensure that only a single thread can initialize the [Lazy] instance.
*/
SYNCHRONIZED,
/**
* Initializer function can be called several times on concurrent access to uninitialized [Lazy] instance value,
* but only first returned value will be used as the value of [Lazy] instance.
*/
PUBLICATION,
/**
* No locks are used to synchronize the access to the [Lazy] instance value; if the instance is accessed from multiple threads, its behavior is undefined.
*
* This mode should be used only when high performance is crucial and the [Lazy] instance is guaranteed never to be initialized from more than one thread.
*/
NONE,
}
private object UNINITIALIZED_VALUE
private class SynchronizedLazyImpl(initializer: () -> T, lock: Any? = null) : Lazy(), Serializable {
private var initializer: (() -> T)? = initializer
@Volatile private var _value: Any? = UNINITIALIZED_VALUE
// final field is required to enable safe publication of constructed instance
private val lock = lock ?: this
override val value: T
get() {
val _v1 = _value
if (_v1 !== UNINITIALIZED_VALUE) {
return _v1 as T
}
return synchronized(lock) {
val _v2 = _value
if (_v2 !== UNINITIALIZED_VALUE) {
_v2 as T
}
else {
val typedValue = initializer!!()
_value = typedValue
initializer = null
typedValue
}
}
}
override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE
override fun toString(): String = if (isInitialized()) value.toString() else "Lazy value not initialized yet."
private fun writeReplace(): Any = InitializedLazyImpl(value)
}
// internal to be called from lazy in JS
internal class UnsafeLazyImpl(initializer: () -> T) : Lazy(), Serializable {
private var initializer: (() -> T)? = initializer
private var _value: Any? = UNINITIALIZED_VALUE
override val value: T
get() {
if (_value === UNINITIALIZED_VALUE) {
_value = initializer!!()
initializer = null
}
return _value as T
}
override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE
override fun toString(): String = if (isInitialized()) value.toString() else "Lazy value not initialized yet."
private fun writeReplace(): Any = InitializedLazyImpl(value)
}
private class InitializedLazyImpl(override val value: T) : Lazy(), Serializable {
override fun isInitialized(): Boolean = true
override fun toString(): String = value.toString()
}
/* Not available on platform: JS */