chore(iter): optimize iterator

Signed-off-by: azjezz <azjezz@protonmail.com>

Author: azjezz

src/Psl/Iter/Iterator.php

@@ -28,9 +28,9 @@ final class Iterator implements Countable, SeekableIterator
     private array $entries = [];
 
     /**
-     * Whether or not the current value/key pair has been added to the local entries.
+     *  Whether or not the current value/key pair has been added to the local entries.
      */
-    private bool $saved = false;
+    private bool $saved = true;
 
     /**
      * Current cursor position for the local entries.
@@ -79,7 +79,7 @@ public static function create(iterable $iterable): Iterator
         /**
          * @var (callable(): Generator<Tsk, Tsv, mixed, void>) $factory
          */
-        $factory = static fn (): Generator => yield from $iterable;
+        $factory = static fn(): Generator => yield from $iterable;
 
         return new self($factory());
     }
@@ -94,34 +94,34 @@ public static function create(iterable $iterable): Iterator
     public function current(): mixed
     {
         Psl\invariant($this->valid(), 'The Iterator is invalid.');
-        if (!contains_key($this->entries, $this->position)) {
-            $this->progress();
-        }
+        $this->save();
 
         return $this->entries[$this->position][1];
     }
 
     /**
-     * Move forward to the next element.
+     * Checks if current position is valid.
      */
-    public function next(): void
+    public function valid(): bool
     {
-        $this->position++;
-        if (null === $this->generator || !$this->generator->valid()) {
-            return;
+        if (isset($this->entries[$this->position])) {
+            return true;
         }
 
-        if (contains_key($this->entries, $this->position + 1)) {
-            return;
+        if (null !== $this->generator && $this->generator->valid()) {
+            return true;
         }
 
-        if (!$this->saved) {
-            $this->progress();
-        }
-        $this->saved = false;
-        $this->generator?->next();
+        $this->generator = null;
+        return false;
+    }
 
-        $this->progress();
+    private function save(): void
+    {
+        if (!$this->saved && $this->generator !== null) {
+            $this->saved = true;
+            $this->entries[] = [$this->generator->key(), $this->generator->current()];
+        }
     }
 
     /**
@@ -134,34 +134,11 @@ public function next(): void
     public function key(): mixed
     {
         Psl\invariant($this->valid(), 'The Iterator is invalid.');
-        if (!contains_key($this->entries, $this->position)) {
-            $this->progress();
-        }
+        $this->save();
 
         return $this->entries[$this->position][0];
     }
 
-    /**
-     * Checks if current position is valid.
-     */
-    public function valid(): bool
-    {
-        if (contains_key($this->entries, $this->position)) {
-            return true;
-        }
-
-        if (null === $this->generator) {
-            return false;
-        }
-
-        if ($this->generator->valid()) {
-            return true;
-        }
-
-        $this->generator = null;
-        return false;
-    }
-
     /**
      * Rewind the Iterator to the first element.
      */
@@ -179,16 +156,18 @@ public function rewind(): void
      */
     public function seek(int $position): void
     {
-        if (0 === $position || $position <= $this->position) {
+        if ($position <= $this->position) {
             $this->position = $position;
             return;
         }
 
         if ($this->generator) {
-            while ($this->position !== $position) {
+            do {
+                $this->save();
                 $this->next();
-                Psl\invariant($this->valid(), 'Position is out-of-bounds.');
-            }
+                /** @psalm-suppress PossiblyNullReference - ->next() and ->save() don't mutate ->generator. */
+                Psl\invariant($this->generator->valid(), 'Position is out-of-bounds.');
+            } while ($this->position < $position);
 
             return;
         }
@@ -199,43 +178,39 @@ public function seek(int $position): void
     }
 
     /**
-     * @return 0|positive-int
-     *
-     * @psalm-suppress MoreSpecificReturnType
+     * Move forward to the next element.
      */
-    public function count(): int
+    public function next(): void
     {
-        if ($this->generator) {
-            $this->exhaust();
+        $this->position++;
+
+        if (isset($this->entries[$this->position]) || null === $this->generator || !$this->generator->valid()) {
+            return;
         }
 
-        /**
-         * @psalm-suppress LessSpecificReturnStatement
-         */
-        return count($this->entries);
+        $this->generator->next();
+        $this->saved = false;
     }
 
-    private function exhaust(): void
+    /**
+     * @return int<0, max>
+     *
+     * @psalm-suppress PossiblyNullReference
+     */
+    public function count(): int
     {
         if ($this->generator) {
-            if ($this->generator->valid()) {
-                foreach ($this->generator as $key => $value) {
-                    $this->entries[] = [$key, $value];
-                }
-            }
+            $previous = $this->position;
+            do {
+                $this->save();
+                $this->next();
+            } while ($this->generator->valid());
+            $this->position = $previous;
 
             $this->generator = null;
         }
-    }
 
-    /**
-     * Save the current key and value to the local entries if the generator is still valid.
-     */
-    private function progress(): void
-    {
-        if ($this->generator && $this->generator->valid() && !$this->saved) {
-            $this->entries[] = [$this->generator->key(), $this->generator->current()];
-            $this->saved     = true;
-        }
+        /** @var int<0, max> */
+        return count($this->entries);
     }
 }

tests/unit/Iter/IteratorTest.php

@@ -129,6 +129,39 @@ public function testIterating(): void
         ], $spy->toArray());
     }
 
+    public function testCountWhileIterating(): void
+    {
+        $spy = new MutableVector([]);
+
+        $generator = (static function () use ($spy): iterable {
+            for ($i = 0; $i < 3; $i++) {
+                $spy->add('sending (' . $i . ')');
+
+                yield ['foo', 'bar'] => $i;
+            }
+        })();
+
+        $rewindable = Iter\rewindable($generator);
+        foreach ($rewindable as $key => $value) {
+            $spy->add('count (' . $rewindable->count() . ')');
+            $spy->add('received (' . $value . ')');
+
+            static::assertSame(['foo', 'bar'], $key);
+        }
+
+        static::assertSame([
+            'sending (0)',
+            'sending (1)',
+            'sending (2)',
+            'count (3)',
+            'received (0)',
+            'count (3)',
+            'received (1)',
+            'count (3)',
+            'received (2)',
+        ], $spy->toArray());
+    }
+
     public function testRewindingValidGenerator(): void
     {
         $spy = new MutableVector([]);