Permalink
Find file Copy path
c53a2d5 Apr 26, 2018
5 contributors

Users who have contributed to this file

@ilya-g @yanex @dzharkov @bashor @udalov
102 lines (79 sloc) 3.2 KB
/*
* Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
* that can be found in the license/LICENSE.txt file.
*/
@file:kotlin.jvm.JvmName("LazyKt")
@file:kotlin.jvm.JvmMultifileClass
package kotlin
import kotlin.reflect.KProperty
/**
* Represents a value with lazy initialization.
*
* To create an instance of [Lazy] use the [lazy] function.
*/
public interface Lazy<out T> {
/**
* Gets the lazily initialized value of the current Lazy instance.
* Once the value was initialized it must not change during the rest of lifetime of this Lazy instance.
*/
public 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 fun isInitialized(): Boolean
}
/**
* Creates a new instance of the [Lazy] that is already initialized with the specified [value].
*/
public fun <T> lazyOf(value: T): Lazy<T> = InitializedLazyImpl(value)
/**
* 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 }`
*/
@kotlin.internal.InlineOnly
public inline operator fun <T> Lazy<T>.getValue(thisRef: Any?, property: KProperty<*>): T = value
/**
* Specifies how a [Lazy] instance synchronizes initialization 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 the first returned value will be used as the value of [Lazy] instance.
*/
PUBLICATION,
/**
* No locks are used to synchronize an access to the [Lazy] instance value; if the instance is accessed from multiple threads, its behavior is undefined.
*
* This mode should not be used unless the [Lazy] instance is guaranteed never to be initialized from more than one thread.
*/
NONE,
}
internal object UNINITIALIZED_VALUE
// internal to be called from lazy in JS
internal class UnsafeLazyImpl<out T>(initializer: () -> T) : Lazy<T>, 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
}
@Suppress("UNCHECKED_CAST")
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)
}
internal class InitializedLazyImpl<out T>(override val value: T) : Lazy<T>, Serializable {
override fun isInitialized(): Boolean = true
override fun toString(): String = value.toString()
}