Add static method ::iterate().

README.md

@@ -130,6 +130,36 @@ Collection::with(
     ->limit(10)
     ->all(); // [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
 
+// or
+
+Collection::iterate(
+    static function($v) {
+        return [$v[1], $v[0] + $v[1]];
+    },
+    [1,1]
+    )
+    ->limit(10)
+    ->all(); // [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+
+// Find the golden ratio with Fibonacci
+$result = Collection::iterate(
+    static function($v) {
+        return [$v[1], $v[0] + $v[1]];
+    },
+    [1,1]
+    )
+    ->map(static function($item) {return $item[0];})
+    ->chunk(2)
+    ->map(
+        static function(ArrayIterator $item) {
+            [$first, $second] = $item;
+
+            return $second / $first;
+        }
+    )
+    ->limit(100)
+    ->last(); // 1.6180339887499
+
 // Use an existing Generator as input data.
 $readFileLineByLine = static function (string $filepath): \Generator {
     $fh = fopen($filepath, 'rb');
@@ -308,6 +338,7 @@ about the kind of parameters they require.
 | Methods       | Return type           | Source         |
 | ------------- | --------------------- | -------------- |
 | `empty`       | new Collection object | [Collection.php](./src/Collection.php)
+| `iterate`     | new Collection object | [Collection.php](./src/Collection.php)
 | `range`       | new Collection object | [Collection.php](./src/Collection.php)
 | `times`       | new Collection object | [Collection.php](./src/Collection.php)
 | `with`        | new Collection object | [Collection.php](./src/Collection.php)

spec/drupol/collection/CollectionSpec.php

@@ -584,6 +584,21 @@ public function it_can_intersperse(): void
             ->during('intersperse', ['foo', 1, -1]);
     }
 
+    public function it_can_iterate(): void
+    {
+        $this
+            ->beConstructedThrough('iterate', [static function ($item) {
+                return [$item[1], $item[0] + $item[1]];
+            }, [0, 1]]);
+
+        $this
+            ->map(static function ($item) {
+                return $item[0];
+            })
+            ->limit(10)
+            ->shouldIterateAs([0, 1, 1, 2, 3, 5, 8, 13, 21, 34]);
+    }
+
     public function it_can_keys(): void
     {
         $this

src/Collection.php

@@ -184,6 +184,26 @@ public function intersperse($element, int $every = 1, int $startAt = 0): BaseInt
         return new Collection($this->run(new Intersperse($element, $every, $startAt)));
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public static function iterate(callable $callback, $initial = null): CollectionInterface
+    {
+        return new Collection(
+            static function () use ($initial, $callback) {
+                $result = $initial;
+
+                yield $initial;
+
+                while (true) {
+                    $result = $callback($result);
+
+                    yield $result;
+                }
+            }
+        );
+    }
+
     /**
      * {@inheritdoc}
      */

src/Contract/Collection.php

@@ -49,6 +49,14 @@ interface Collection extends
      */
     public static function empty(): Collection;
 
+    /**
+     * @param callable $callback
+     * @param mixed $initial
+     *
+     * @return \drupol\collection\Contract\Collection
+     */
+    public static function iterate(callable $callback, $initial = null): Collection;
+
     /**
      * Create a new with a range of number.
      *
@@ -69,4 +77,12 @@ public static function range(int $start = 0, $end = \INF, $step = 1): Collection
      * @return \drupol\collection\Contract\Collection
      */
     public static function times($number, callable $callback = null): Collection;
+
+    /**
+     * @param callable $callback
+     * @param mixed $initial
+     *
+     * @return \drupol\collection\Contract\Collection
+     */
+    public static function iterate(callable $callback, $initial = null): Collection;
 }