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| 1 | +.. index:: |
| 2 | + single: ClassLoader; PSR-4 Class Loader |
| 3 | + |
| 4 | +The PSR-4 Class Loader |
| 5 | +====================== |
| 6 | + |
| 7 | +Libraries that follow the `PSR-4`_ standard can be loaded with the ``Psr4ClassLoader``. |
| 8 | + |
| 9 | +.. note:: |
| 10 | + |
| 11 | + If you manage your dependencies via Composer, you get a PSR-4 compatible |
| 12 | + autoloader out of the box. Use this loader in environments where Composer |
| 13 | + is not available. |
| 14 | + |
| 15 | +.. tip:: |
| 16 | + All Symfony Components follow PSR-4. |
| 17 | + |
| 18 | +Usage |
| 19 | +----- |
| 20 | + |
| 21 | +The following example demonstrates, how you can use the |
| 22 | +:class:`Symfony\\Component\\ClassLoader\\Psr4ClassLoader` autoloader to use |
| 23 | +Symfony's Yaml component. Let's imagine, you downloaded both components – |
| 24 | +ClassLoader and Yaml – as ZIP packages and unpacked them to a libs directory. |
| 25 | + |
| 26 | +The directory structure will look like this: |
| 27 | + |
| 28 | +.. code-block:: text |
| 29 | +
|
| 30 | + / |
| 31 | + +- libs |
| 32 | + | +- ClassLoader |
| 33 | + | | +- Psr4ClassLoader.php |
| 34 | + | | +- … |
| 35 | + | +- Yaml |
| 36 | + | +- Yaml.php |
| 37 | + | +- … |
| 38 | + +- config.yml |
| 39 | + +- test.php |
| 40 | +
|
| 41 | +In ``demo.php``, to parse the file ``config.yml``, you can use the following |
| 42 | +code. |
| 43 | + |
| 44 | +.. code-block:: php |
| 45 | +
|
| 46 | + use Symfony\Component\ClassLoader\Psr4ClassLoader; |
| 47 | + use Symfony\Component\Yaml\Yaml; |
| 48 | +
|
| 49 | + require __DIR__ . '/lib/ClassLoader/Psr4ClassLoader.php'; |
| 50 | +
|
| 51 | + $loader = new Psr4ClassLoader(); |
| 52 | + $loader->addPrefix('Symfony\\Component\\Yaml\\', __DIR__ . '/lib/Yaml'); |
| 53 | + $loader->register(); |
| 54 | +
|
| 55 | + $data = Yaml::parse(__DIR__ . '/demo.yml'); |
| 56 | +
|
| 57 | +First of all, we've loaded our class loader manually using ``require`` since we |
| 58 | +don't have an autoload mechanism, yet. With the ``addPrefix()`` call, we told |
| 59 | +the class loader where to look for classes with the namespace prefix |
| 60 | +``Symfony\Component\Yaml\``. After registering the autoloader, the Yaml |
| 61 | +component is ready to use. |
| 62 | + |
| 63 | +.. _PSR-4: http://www.php-fig.org/psr/psr-4/ |
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