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Iterables.kt
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Iterables.kt
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/*
* 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.JvmMultifileClass
@file:kotlin.jvm.JvmName("CollectionsKt")
package kotlin.collections
/**
* Given an [iterator] function constructs an [Iterable] instance that returns values through the [Iterator]
* provided by that function.
* @sample samples.collections.Iterables.Building.iterable
*/
@kotlin.internal.InlineOnly
public inline fun <T> Iterable(crossinline iterator: () -> Iterator<T>): Iterable<T> = object : Iterable<T> {
override fun iterator(): Iterator<T> = iterator()
}
/**
* A wrapper over another [Iterable] (or any other object that can produce an [Iterator]) that returns
* an indexing iterator.
*/
internal class IndexingIterable<out T>(private val iteratorFactory: () -> Iterator<T>) : Iterable<IndexedValue<T>> {
override fun iterator(): Iterator<IndexedValue<T>> = IndexingIterator(iteratorFactory())
}
/**
* Returns the size of this iterable if it is known, or `null` otherwise.
*/
@PublishedApi
internal fun <T> Iterable<T>.collectionSizeOrNull(): Int? = if (this is Collection<*>) this.size else null
/**
* Returns the size of this iterable if it is known, or the specified [default] value otherwise.
*/
@PublishedApi
internal fun <T> Iterable<T>.collectionSizeOrDefault(default: Int): Int = if (this is Collection<*>) this.size else default
/** Returns true when it's safe to convert this collection to a set without changing contains method behavior. */
private fun <T> Collection<T>.safeToConvertToSet() = size > 2 && this is ArrayList
/** Converts this collection to a set, when it's worth so and it doesn't change contains method behavior. */
internal fun <T> Iterable<T>.convertToSetForSetOperationWith(source: Iterable<T>): Collection<T> =
when (this) {
is Set -> this
is Collection ->
when {
source is Collection && source.size < 2 -> this
else -> if (this.safeToConvertToSet()) toHashSet() else this
}
else -> toHashSet()
}
/** Converts this collection to a set, when it's worth so and it doesn't change contains method behavior. */
internal fun <T> Iterable<T>.convertToSetForSetOperation(): Collection<T> =
when (this) {
is Set -> this
is Collection -> if (this.safeToConvertToSet()) toHashSet() else this
else -> toHashSet()
}
/**
* Returns a single list of all elements from all collections in the given collection.
* @sample samples.collections.Iterables.Operations.flattenIterable
*/
public fun <T> Iterable<Iterable<T>>.flatten(): List<T> {
val result = ArrayList<T>()
for (element in this) {
result.addAll(element)
}
return result
}
/**
* Returns a pair of lists, where
* *first* list is built from the first values of each pair from this collection,
* *second* list is built from the second values of each pair from this collection.
* @sample samples.collections.Iterables.Operations.unzipIterable
*/
public fun <T, R> Iterable<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> {
val expectedSize = collectionSizeOrDefault(10)
val listT = ArrayList<T>(expectedSize)
val listR = ArrayList<R>(expectedSize)
for (pair in this) {
listT.add(pair.first)
listR.add(pair.second)
}
return listT to listR
}