a

src/main/kotlin/ru/dbotthepony/mc/otm/core/collect/StreamyIterators.kt

@@ -25,8 +25,7 @@ import java.util.stream.StreamSupport
 
 // Aside parallel work, unimplemented Stream API elements can be easily implemented when required
 
-private class FilteringIterator<T>(private val parent: Iterator<T>, private val predicate: Predicate<in T>) : MutableIterator<T> {
-	private var value: T = parent.next()
+private class FilteringIterator<T>(private val parent: Iterator<T>, private val predicate: Predicate<in T>, private var value: T) : MutableIterator<T> {
 	private var hasValue = true
 	private var returned = false
 
@@ -78,23 +77,26 @@ private class MappingIterator<T, R>(private val parent: Iterator<T>, private val
 private class FlatMappingIterator<T, R>(private val parent: Iterator<T>, private val mapper: (T) -> Iterator<R>) : MutableIterator<R> {
 	private var current: Iterator<R> = mapper.invoke(parent.next())
 	private var last: Iterator<R>? = null
-	private var hasNext = current.hasNext()
+
+	init {
+		while (!current.hasNext() && parent.hasNext()) {
+			current = mapper.invoke(parent.next())
+		}
+	}
 
 	override fun hasNext(): Boolean {
-		return hasNext
+		return current.hasNext()
 	}
 
 	override fun next(): R {
-		if (!hasNext)
+		if (!current.hasNext())
 			throw NoSuchElementException()
 
 		val v = current.next()
 		last = current
-		hasNext = false
 
-		while (!hasNext && parent.hasNext()) {
+		while (!current.hasNext() && parent.hasNext()) {
 			current = mapper.invoke(parent.next())
-			hasNext = current.hasNext()
 		}
 
 		return v
@@ -183,11 +185,15 @@ fun <T> concatIterators(vararg iterators: Iterator<T>): MutableIterator<T> {
  * Resulting [Iterator] is [MutableIterator] if [this] is
  */
 fun <T> Iterator<T>.filter(condition: Predicate<in T>): MutableIterator<T> {
-	if (!hasNext()) {
-		return emptyIterator()
+	while (hasNext()) {
+		val v = next()
+
+		if (condition.test(v)) {
+			return FilteringIterator(this, condition, v)
+		}
 	}
 
-	return FilteringIterator(this, condition)
+	return emptyIterator()
 }
 
 /**