Add IfThenElse operation.

docs/pages/api.rst

@@ -627,6 +627,37 @@ Signature: ``Collection::head();``
     Collection::fromIterable($generator())
         ->head(); // [1 => 'a']
 
+ifThenElse
+~~~~~~~~~~
+
+Execute a callback when a condition is met.
+
+Interface: `IfThenElseable`_
+
+Signature: ``Collection::ifThenElse(callable $condition, callable $then, ?callable $else = null);``
+
+.. code-block:: php
+
+    $input = range(1, 5);
+
+    $condition = static function (int $value): bool {
+        return 0 === $value % 2;
+    };
+
+    $then = static function (int $value): int {
+        return $value * $value;
+    };
+
+    $else = static function (int $value): int {
+        return $value + 2;
+    };
+
+    Collection::fromIterable($input)
+        ->ifThenElse($condition, $then); // [1, 4, 3, 16, 5]
+
+    Collection::fromIterable($input)
+        ->ifThenElse($condition, $then, $else) // [3, 4, 5, 16, 7]
+
 intersect
 ~~~~~~~~~
 
@@ -1516,6 +1547,7 @@ Interface: `Truthyable`_
 .. _Groupable: https://github.com/loophp/collection/blob/master/src/Contract/Operation/Groupable.php
 .. _Hasable: https://github.com/loophp/collection/blob/master/src/Contract/Transformation/Hasable.php
 .. _Headable: https://github.com/loophp/collection/blob/master/src/Contract/Operation/Headable.php
+.. _IfThenElseable: https://github.com/loophp/collection/blob/master/src/Contract/Operation/IfThenElseable.php
 .. _Implodeable: https://github.com/loophp/collection/blob/master/src/Contract/Transformation/Implodeable.php
 .. _Intersectable: https://github.com/loophp/collection/blob/master/src/Contract/Operation/Intersectable.php
 .. _Intersectkeysable: https://github.com/loophp/collection/blob/master/src/Contract/Operation/Intersectkeysable.php

spec/loophp/collection/CollectionSpec.php

@@ -1043,6 +1043,35 @@ public function it_can_head(): void
             ->shouldIterateAs([0 => 'A']);
     }
 
+    public function it_can_if_then_else()
+    {
+        $input = range(1, 5);
+
+        $condition = static function ($value) {
+            return 0 === $value % 2;
+        };
+
+        $then = static function ($value) {
+            return $value * $value;
+        };
+
+        $else = static function ($value) {
+            return $value + 2;
+        };
+
+        $this::fromIterable($input)
+            ->ifThenElse($condition, $then)
+            ->shouldIterateAs([
+                1, 4, 3, 16, 5,
+            ]);
+
+        $this::fromIterable($input)
+            ->ifThenElse($condition, $then, $else)
+            ->shouldIterateAs([
+                3, 4, 5, 16, 7,
+            ]);
+    }
+
     public function it_can_implode(): void
     {
         $this::fromIterable(range('A', 'C'))

src/Collection.php

@@ -36,6 +36,7 @@
 use loophp\collection\Operation\Frequency;
 use loophp\collection\Operation\Group;
 use loophp\collection\Operation\Head;
+use loophp\collection\Operation\IfThenElse;
 use loophp\collection\Operation\Intersect;
 use loophp\collection\Operation\IntersectKeys;
 use loophp\collection\Operation\Intersperse;
@@ -432,6 +433,15 @@ public function head(): CollectionInterface
         return $this->run(new Head());
     }
 
+    public function ifThenElse(callable $condition, callable $then, ?callable $else = null): CollectionInterface
+    {
+        $else = $else ?? static function ($value, $key) {
+            return $value;
+        };
+
+        return $this->run(new IfThenElse($condition, $then, $else));
+    }
+
     public function implode(string $glue = ''): string
     {
         return $this->transform(new Implode($glue));

src/Contract/Collection.php

@@ -29,6 +29,7 @@
 use loophp\collection\Contract\Operation\Frequencyable;
 use loophp\collection\Contract\Operation\Groupable;
 use loophp\collection\Contract\Operation\Headable;
+use loophp\collection\Contract\Operation\IfThenElseable;
 use loophp\collection\Contract\Operation\Intersectable;
 use loophp\collection\Contract\Operation\Intersectkeysable;
 use loophp\collection\Contract\Operation\Intersperseable;
@@ -117,6 +118,7 @@
  * @template-extends Groupable<TKey, T>
  * @template-extends Hasable<TKey, T>
  * @template-extends Headable<TKey, T>
+ * @template-extends IfThenElseable<TKey, T>
  * @template-extends Intersectable<TKey, T>
  * @template-extends Intersectkeysable<TKey, T>
  * @template-extends Intersperseable<TKey, T>
@@ -190,6 +192,7 @@ interface Collection extends
     Groupable,
     Hasable,
     Headable,
+    IfThenElseable,
     Implodeable,
     Intersectable,
     Intersectkeysable,

src/Contract/Operation/IfThenElseable.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace loophp\collection\Contract\Operation;
+
+use loophp\collection\Contract\Collection;
+
+/**
+ * @psalm-template TKey
+ * @psalm-template TKey of array-key
+ * @psalm-template T
+ */
+interface IfThenElseable
+{
+    /**
+     * @psalm-return \loophp\collection\Contract\Collection<TKey, T>
+     */
+    public function ifThenElse(callable $condition, callable $then, ?callable $else = null): Collection;
+}

src/Operation/IfThenElse.php

@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace loophp\collection\Operation;
+
+use Closure;
+use Generator;
+use Iterator;
+use loophp\collection\Contract\Operation;
+
+/**
+ * @psalm-template TKey
+ * @psalm-template TKey of array-key
+ * @psalm-template T
+ */
+final class IfThenElse extends AbstractOperation implements Operation
+{
+    /**
+     * @psalm-param callable(T, TKey): bool $condition
+     * @psalm-param callable(T, TKey): (T|TKey) $then
+     * @psalm-param callable(T, TKey): (T|TKey) $else
+     */
+    public function __construct(callable $condition, callable $then, callable $else)
+    {
+        $this->storage = [
+            'condition' => $condition,
+            'then' => $then,
+            'else' => $else,
+        ];
+    }
+
+    // phpcs:disable
+    /**
+     * @psalm-return Closure(Iterator<TKey, T>, callable(T, TKey): bool, callable(T, TKey): (T|TKey), callable(T, TKey): (T|TKey)): Generator<TKey, T>
+     */
+    // phpcs:enable
+    public function __invoke(): Closure
+    {
+        return static function (Iterator $iterator, callable $condition, callable $then, callable $else): Generator {
+            foreach ($iterator as $key => $value) {
+                yield $key => $condition($value, $key) ?
+                    $then($value, $key) :
+                    $else($value, $key);
+            }
+        };
+    }
+}