Use iterable instead of \Traversable.

README.md

@@ -129,6 +129,41 @@ Collection::with(
     )
     ->limit(10)
     ->all(); // [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+
+// Use an existing Generator as input data.
+$readFileLineByLine = static function (string $filepath): \Generator {
+    $fh = fopen($filepath, 'rb');
+    $i = 0;
+
+    while (!feof($fh)) {
+        $line = '';
+
+        while (PHP_EOL !== $chunk = fread($fh, 1)) {
+            $line .= $chunk;
+        }
+
+        yield [
+            'number' => $i++,
+            'content' => $line
+        ];
+    }
+
+    fclose($fh);
+};
+
+$hugeFile = __DIR__ .'/vendor/composer/autoload_static.php';
+
+Collection::with($readFileLineByLine($hugeFile))
+    // Find public static fields or methods.
+    ->filter(static function (array $line) {return false !== strpos($line['content'], 'public static');})
+    // Skip the first one.
+    ->skip(1)
+    // Limit the list to 3 results only.
+    ->limit(3)
+    // Add the line number at the end of each line.
+    ->map(static function (array $line) {return sprintf('%s // Line %s', $line['content'], $line['number']);})
+    // Implode into a string.
+    ->implode(PHP_EOL);
 ```
 
 ## Advanced usage
@@ -153,7 +188,7 @@ $square = new class() extends Operation {
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection): \Closure
+    public function on(iterable $collection): \Closure
     {
         return static function () use ($collection) {
                 foreach ($collection as $item) {

spec/drupol/collection/CollectionSpec.php

@@ -276,6 +276,10 @@ public function it_can_contains(): void
             ->contains('A')
             ->shouldReturn(true);
 
+        $this
+            ->contains('unknown')
+            ->shouldReturn(false);
+
         $this
             ->contains(static function ($item) {
                 return 'A' === $item;
@@ -756,7 +760,7 @@ static function ($carry, $item) {
     public function it_can_run_an_operation(Operation $operation): void
     {
         $square = new class() extends \drupol\collection\Operation\Operation {
-            public function on(\Traversable $collection)
+            public function on(iterable $collection)
             {
                 return Collection::with(
                     static function () use ($collection) {
@@ -769,7 +773,7 @@ static function () use ($collection) {
         };
 
         $sqrt = new class() extends \drupol\collection\Operation\Operation {
-            public function on(\Traversable $collection)
+            public function on(iterable $collection)
             {
                 return Collection::with(
                     static function () use ($collection) {
@@ -782,7 +786,7 @@ static function () use ($collection) {
         };
 
         $map = new class() extends \drupol\collection\Operation\Operation {
-            public function on(\Traversable $collection)
+            public function on(iterable $collection)
             {
                 return Collection::with(
                     static function () use ($collection) {

spec/drupol/collection/Iterator/ClosureIteratorSpec.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace spec\drupol\collection\Iterator;
+
+use drupol\collection\Iterator\ClosureIterator;
+use PhpSpec\ObjectBehavior;
+
+class ClosureIteratorSpec extends ObjectBehavior
+{
+    public function it_can_be_constructed_with_a_callable_which_is_not_a_generator(): void
+    {
+        $callback = static function () {
+            return \range(1, 5);
+        };
+
+        $this
+            ->beConstructedWith($callback);
+    }
+
+    public function it_can_get_a_key(): void
+    {
+        $callback = static function () {
+            return \range(1, 5);
+        };
+
+        $this
+            ->beConstructedWith($callback);
+
+        $this
+            ->key()
+            ->shouldReturn(0);
+    }
+
+    public function it_can_send(): void
+    {
+        $callback = static function () {
+            yield from \range(1, 5);
+        };
+
+        $this
+            ->beConstructedWith($callback);
+
+        $this->send('foo');
+    }
+
+    public function it_can_use_next(): void
+    {
+        $callback = static function () {
+            return \range(1, 5);
+        };
+
+        $this
+            ->beConstructedWith($callback);
+
+        $this
+            ->next()
+            ->shouldReturn($this);
+
+        $this
+            ->current()
+            ->shouldReturn(2);
+    }
+
+    public function it_is_initializable(): void
+    {
+        $callback = static function ($a, $b, $c) {
+            yield $a;
+
+            yield $b;
+
+            yield $c;
+        };
+
+        $this
+            ->beConstructedWith($callback, 'foo', 'bar', 'baz');
+
+        $this->shouldHaveType(ClosureIterator::class);
+
+        $this
+            ->current()
+            ->shouldBeEqualTo('foo');
+    }
+}

src/BaseCollection.php

@@ -29,7 +29,7 @@ public function __construct($data = [])
                 $this->source = $data;
 
                 break;
-            case $data instanceof \Traversable:
+            case \is_iterable($data):
                 $this->source = static function () use ($data) {
                     foreach ($data as $k => $v) {
                         yield $k => $v;

src/Contract/Operation.php

@@ -10,9 +10,9 @@
 interface Operation
 {
     /**
-     * @param \Traversable $collection
+     * @param iterable $collection
      *
      * @return mixed
      */
-    public function on(\Traversable $collection);
+    public function on(iterable $collection);
 }

src/Iterator/ClosureIterator.php

@@ -22,93 +22,97 @@ class ClosureIterator implements \Iterator
     /**
      * ClosureIterator constructor.
      *
-     * @param \Closure $closure
-     *
-     * @throws \ReflectionException
+     * @param callable $callable
+     * @param array ...$arguments
      */
-    public function __construct(\Closure $closure)
+    public function __construct(callable $callable, ...$arguments)
     {
-        $reflection = new \ReflectionFunction($closure);
-
-        if (!$reflection->isGenerator()) {
-            $closure = static function () use ($closure) {
-                foreach ($closure() as $k => $v) {
-                    yield $k => $v;
-                }
-            };
-        }
-
-        $this->source = static function () use ($closure) {
-            foreach ($closure() as $k => $v) {
+        $this->source = static function () use ($callable, $arguments) {
+            foreach ($callable(...$arguments) as $k => $v) {
                 yield $k => $v;
             }
         };
-
-        $this->generator = $closure();
     }
 
     /**
-     * Return the current element.
+     * {@inheritdoc}
      *
-     * @see https://php.net/manual/en/iterator.current.php
-     *
-     * @return mixed Can return any type.
-     *
-     * @since 5.0.0
+     * @return mixed
      */
     public function current()
     {
+        if (null === $this->generator) {
+            $this->rewind();
+        }
+
         return $this->generator->current();
     }
 
     /**
-     * Return the key of the current element.
-     *
-     * @see https://php.net/manual/en/iterator.key.php
-     *
-     * @return mixed scalar on success, or null on failure.
+     * {@inheritdoc}
      *
-     * @since 5.0.0
+     * @return int|string
      */
     public function key()
     {
+        if (null === $this->generator) {
+            $this->rewind();
+        }
+
         return $this->generator->key();
     }
 
     /**
-     * Move forward to next element.
+     * {@inheritdoc}
      *
-     * @see https://php.net/manual/en/iterator.next.php
-     * @since 5.0.0
+     * @return $this|void
      */
-    public function next(): void
+    public function next()
     {
+        if (null === $this->generator) {
+            $this->rewind();
+        }
+
         $this->generator->next();
+
+        return $this;
     }
 
     /**
-     * Rewind the Iterator to the first element.
-     *
-     * @see https://php.net/manual/en/iterator.rewind.php
-     * @since 5.0.0
+     * {@inheritdoc}
      */
     public function rewind(): void
     {
         $this->generator = ($this->source)();
     }
 
     /**
-     * Checks if current position is valid.
+     * Send a value to the inner Generator.
      *
-     * @see https://php.net/manual/en/iterator.valid.php
+     * @param null|mixed $value
      *
-     * @return bool The return value will be casted to boolean and then evaluated.
-     * Returns true on success or false on failure.
+     * @return mixed
+     */
+    public function send($value = null)
+    {
+        if (null === $this->generator) {
+            $this->rewind();
+        }
+
+        return $this->generator->send($value);
+    }
+
+    /**
+     * {@inheritdoc}
      *
-     * @since 5.0.0
+     * @return bool
      */
     public function valid()
     {
+        if (null === $this->generator) {
+            $this->rewind();
+        }
+
         return $this->generator->valid();
     }
 }

src/Operation/All.php

@@ -20,7 +20,7 @@ public function __construct()
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection)
+    public function on(iterable $collection)
     {
         $result = [];
 

src/Operation/Append.php

@@ -12,7 +12,7 @@ final class Append extends Operation
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection): \Closure
+    public function on(iterable $collection): \Closure
     {
         [$items] = $this->parameters;
 

src/Operation/Apply.php

@@ -12,7 +12,7 @@ final class Apply extends Operation
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection): \Traversable
+    public function on(iterable $collection): iterable
     {
         [$callbacks] = $this->parameters;
 

src/Operation/Chunk.php

@@ -24,12 +24,12 @@ public function __construct(int $size)
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection): \Closure
+    public function on(iterable $collection): \Closure
     {
         [$size] = $this->parameters;
 
         if (0 >= $size) {
-            return static function () {
+            return static function (): \Generator {
                 yield from [];
             };
         }
@@ -50,7 +50,7 @@ static function () use ($collection) {
                     $values[$iterator->key()] = $iterator->current();
                 }
 
-                yield new \ArrayObject($values);
+                yield new \ArrayIterator($values);
             }
         };
     }

src/Operation/Collapse.php

@@ -12,7 +12,7 @@ final class Collapse extends Operation
     /**
      * {@inheritdoc}
      */
-    public function on(\Traversable $collection): \Closure
+    public function on(iterable $collection): \Closure
     {
         return static function () use ($collection): \Generator {
             foreach ($collection as $item) {