41 lines
1.5 KiB
Kotlin
41 lines
1.5 KiB
Kotlin
package moe.kageru.sekwences
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/**
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* Sequence that holds a [CoalescingIterator].
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*/
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internal class CoalescingSequence<T>(private val source: Sequence<T>, private inline val merger: (T, T) -> T?) : Sequence<T> {
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override fun iterator(): Iterator<T> {
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return CoalescingIterator(source.iterator(), merger)
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}
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/**
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* Iterator that will attempt to merge adjacent elements as described in the KDoc for [coalesce].
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*/
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internal class CoalescingIterator<T>(private val source: Iterator<T>, private inline val merger: (T, T) -> T?) : Iterator<T> {
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private var previous: T = if (source.hasNext()) source.next() else error("Please don’t pass empty iterators in here")
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// The reason we need this marker is that our iterator can still hold one value, even if the source has been drained.
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private var hasNext = true
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override fun hasNext() = hasNext
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override tailrec fun next(): T {
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if (!source.hasNext()) {
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hasNext = false
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return previous
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}
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val current = source.next()
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val merged = merger(previous, current)
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// If the elements can’t be merged, return the first, then save the second for next time.
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return if (merged == null) {
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val ret = previous
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previous = current
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ret
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} else {
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previous = merged
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next()
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}
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}
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}
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} |