add mapping adapter

README.md

@@ -333,6 +333,26 @@ $results = array(/* ... */);
 $adapter = new FixedAdapter($nbResults, $results);
 ```
 
+### MappingAdapter
+
+This adapter allows you to define a callback to be applied to all items coming out of the adapter.
+Useful when you need to do something simple to the items that you only need to do when they 
+are paginated.
+
+```php
+<?php
+
+use Pagerfanta\Adapter\MappingAdapter;
+
+$results = array(/* ... */);
+
+$adapter = new MappingAdapter(new ArrayAdapter($results), function (array $items) {
+   return array_map(function ($item) {
+       return $item + 1;
+   }, $items);
+});
+```
+
 ## Views
 
 Views are to render pagerfantas, this way you can reuse your

src/Pagerfanta/Adapter/MappingAdapter.php

@@ -0,0 +1,48 @@
+<?php
+
+/*
+ * This file is part of the Pagerfanta package.
+ *
+ * (c) Pablo Díez <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Pagerfanta\Adapter;
+
+class MappingAdapter implements AdapterInterface
+{
+    private $innerAdapter;
+    private $callback;
+
+    /**
+     * @param AdapterInterface $innerAdapter
+     * @param callable $callback
+     */
+    public function __construct(AdapterInterface $innerAdapter, $callback)
+    {
+        if (!is_callable($callback)) {
+            throw new \InvalidArgumentException('$callback must be callable');
+        }
+
+        $this->innerAdapter = $innerAdapter;
+        $this->callback = $callback;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getNbResults()
+    {
+        return $this->innerAdapter->getNbResults();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getSlice($offset, $length)
+    {
+        return call_user_func($this->callback, $this->innerAdapter->getSlice($offset, $length));
+    }
+}

tests/Pagerfanta/Tests/Adapter/MappingAdapterTest.php

@@ -0,0 +1,72 @@
+<?php
+
+/*
+ * This file is part of the Pagerfanta package.
+ *
+ * (c) Pablo Díez <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Pagerfanta\Tests\Adapter;
+
+use Pagerfanta\Adapter\ArrayAdapter;
+use Pagerfanta\Adapter\MappingAdapter;
+
+class MappingAdapterTest extends \PHPUnit_Framework_TestCase
+{
+    /** @var  MappingAdapter */
+    protected $adapter;
+
+    public function setUp()
+    {
+        $this->adapter = new MappingAdapter(new ArrayAdapter(array(
+            34,
+            45,
+            67,
+            12
+        )), function (array $items) {
+            return array_map(
+                function ($item) {
+                    return $item + 1;
+                },
+                $items
+            );
+        });
+    }
+
+    public function testGetNbResults()
+    {
+        $this->assertEquals(4, $this->adapter->getNbResults());
+    }
+
+    public function testGetSlice()
+    {
+        $this->assertEquals(array(
+            35,
+            46,
+            68,
+            13
+        ), $this->adapter->getSlice(0, 34));
+        $this->assertEquals(array(
+            35,
+            46,
+        ), $this->adapter->getSlice(0, 2));
+        $this->assertEquals(array(
+            68,
+            13,
+        ), $this->adapter->getSlice(2, 5));
+        $this->assertEquals(array(
+            68,
+        ), $this->adapter->getSlice(2, 1));
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     */
+    public function testConstructorWithNonCallableForCallback()
+    {
+        new MappingAdapter(new ArrayAdapter(array()), 'bla');
+    }
+}