Autoloading on Autopilot

Autoloading is a wonderful feature in PHP that allows you to automatically include the files that your classes are in as they are referenced. Let's talk about how it works, how to do it, and all that goes with it, including namespaces, PSR standards, and Composer. Hopefully by the end of this discussion, autoloading will be so easy for you that it will feel like it's on autopilot.

Transcript

1. Autoloading on Autopilot
   by Jeremy Lindblom (@jeremeamia)
   

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2. About Me
   @jeremeamia
   

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3. ● Includes
   ● Autoloaders
   ● Optimization
   ● Namespaces
   ● PSRs
   ● Composer
   Autoloading on Autopilot
   

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4. — Includes —
   

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5. a.php
   CODE
   CODE
   include ‘b.php’;
   CODE
   Includes = Why I Started Using PHP
   b.php
   CODE
   CODE
   CODE
   CODE
   Executed code
   CODE
   CODE
   CODE
   CODE
   CODE
   CODE
   CODE
   

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6. Includes = Why I Started Using PHP
   header.php
   sidebar.php main.php
   

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8. include
   include_once
   require
   require_once
   Including vs. Requiring
   What’s the difference
   between all of these?
   

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9. include
   include_once
   require
   require_once
   Including vs. Requiring
   On errors:
   include ➔ E_WARNING
   require ➔ E_COMPILE_ERROR
   “once”:
   Only loads file if you haven’t
   loaded it before.
   

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10. Including Classes - Not Fun
    // NOTE: Assuming one class per file
    require_once(‘classes/user.class.php’);
    require_once(‘classes/page.class.php’);
    require_once(‘classes/role.class.php’);
    require_once(‘classes/db.class.php’);
    // ...
    

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11. The Bottom Line
    Explicit includes/requires are:
    1. Necessary and helpful for
    procedural code.
    2. Cumbersome and harmful for object-
    oriented code.
    

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12. — Autoloaders —
    

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13. What is an Autoloader?
    1. A callback triggered when a non-existent
    class is referenced.
    

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14. What is an Autoloader?
    1. A callback triggered when a non-existent
    class is referenced.
    2. A function that provides a definition for a
    specified class name.
    

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15. What is an Autoloader?
    1. A callback triggered when a non-existent
    class is referenced.
    2. A function that provides a definition for a
    specified class name.
    “Providing a definition” can mean:
    ● Loading a class from a file (include/require)
    ● Dynamically creating a class (eval)
    ● Aliasing an existing class (class_alias)
    

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16. Autoloader Advantages
    ● Classes are loaded on demand
    ○ No need to write specific include statements
    ○ Class never loaded unless it’s needed
    ● Leads to better code maintainability
    ● Easy to write
    

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17. The Old Way – Includes everywhere
    require_once(‘classes/user.class.php’);
    require_once(‘classes/page.class.php’);
    // ...
    $page = Page::forTemplate(‘profile’);
    $page->set(‘user’, User::fetchById(5));
    

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18. Autoloading to the Rescue
    function __autoload($class) {
    $file = strtolower($class).‘.class.php’;
    require(‘classes/’.$file);
    }
    $page = Page::forTemplate(‘profile’);
    $page->set(‘user’, User::fetchById(5));
    

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19. Autoloading to the Rescue
    function __autoload($class) {
    $file = strtolower($class).‘.class.php’;
    require(‘classes/’.$file);
    }
    $page = Page::forTemplate(‘profile’);
    $page->set(‘user’, User::fetchById(5));
    WHY NOT USE require_once?
    

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20. Implicit “Once”
    Autoloaders are only triggered if the specified
    class is not loaded,
    So…
    The “_once” is implied, since once you load a
    class, the autoloader won’t be called again.
    

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21. Implicit “Once”
    No need for these:
    ● include_once
    ● require_once
    Don’t use them anymore for loading classes.
    

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22. function __autoload($class) {
    $file = strtolower($class).‘.class.php’;
    require(‘classes/’.$file);
    }
    SOMETHING IS STILL WRONG WITH THIS CODE.
    

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23. function __autoload($class) {
    $file = strtolower($class).‘.class.php’;
    require(‘classes/’.$file);
    } YOU SHOULD NOT USE
    THIS FUNCTION
    SOMETHING IS STILL WRONG WITH THIS CODE.
    

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24. Please Use spl_autoload_register
    ● Added in PHP 5.1.2
    ● Can register multiple autoloaders
    ○ Allows third-party libraries to provide their own!
    ● Can add an autoloader to the front or back
    of the autoloader queue
    ● Any use of __autoload gets superceded by
    spl_autoload_register
    

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25. Please Use spl_autoload_register
    spl_autoload_register(function ($c) {
    if ($c === ‘Foo’) require ‘lib/foo.inc’;
    });
    spl_autoload_register(function ($c) {
    $path = ‘classes/’.strtolower($c).‘.class.php’;
    if (file_exists($path)) require $path;
    });
    

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26. Errors in Autoloaders
    Do not throw exceptions or trigger
    errors in an autoloader.
    Give the rest of the chain a chance.
    

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27. — Optimization —
    

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28. BAD
    GOOD
    There are many ways to implement autoloaders.
    

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29. All classes in one file; no autoloader
    BAD
    GOOD
    

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30. Many autoloaders; Each can only load 1 class
    BAD
    GOOD
    

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31. BAD
    GOOD
    2 1
    

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32. — Namespaces —
    

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33. Namespaces
    ● Added in PHP 5.3
    ● Prevents naming collisions
    ● Syntax:
    ○ Before Namespaces: Zend_Http_Client
    ○ With Namespaces: Zend\Http\Client
    ● Allows aliasing
    

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34. Namespaces - Defining
    namespace Zend\Http;
    class Client {
    // ...
    }
    

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35. Namespaces - Using
    namespace SeaPhp\Example;
    use My\Orange\Carrot;
    use Foo\Bar as Bunny;
    $thing = new Bunny(new Carrot);
    

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37. — PSRs & PHP-FIG —
    

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38. ● FIG = Framework Interop Group
    ● PSR - PHP Standards Recommendation
    ○ Autoloading: PSR-0, PSR-4
    ○ Others:
    ■ PSR-1, PSR-2 - Coding style
    ■ PSR-3 - Logging interface
    ■ PSR-7 - HTTP message interface
    PHP-FIG
    

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40. Given class:
    Zend\Http\Client
    Load file:
    /Zend/Http/Client.php
    Autoloading PSRs
    

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41. Example Implementation (incomplete)
    spl_autoload_register(function ($class) {
    $path = str_replace(‘\\’, ‘/’, $class);
    if (file_exists($path)) require $path;
    });
    

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42. — Composer —
    

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43. Composer - “Dependency Manager for PHP”
    ● Installs dependencies (a.k.a.
    third-party libraries) into
    your project.
    ● Creates an autoloader
    capable of autoloading
    everything in your project.
    

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44. Setting up Autoloading w/ Composer
    Your files:
    Project/
    |- README
    |- composer.json
    |- src/
    |- Foo.php (contains SeaPhp\Example\Foo)
    |- Bar.php (contains SeaPhp\Example\Bar)
    

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45. Setting up Autoloading w/ Composer
    In your composer.json:
    ...
    "autoload": {
    "psr-4": {
    "SeaPhp\\Example\\": "src/"
    }
    }
    

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46. Autoloading on Autopilot w/ Composer
    In your project root:
    $ composer.phar install
    

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47. Autoloading on Autopilot w/ Composer
    In your index.php:
    require ‘vendor/autoload.php’;
    use SeaPhp\Example\Foo;
    $foo = new Foo;
    

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49. — Optimization —
    (Revisited)
    

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50. BAD
    GOOD
    2 1
    

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51. BAD
    GOOD
    Composer autoloader
    (1 autoloader handles all classes)
    

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52. Classmap Autoloading
    In your project root:
    $ composer.phar dumpautoload -o
    

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53. Classmap Autoloading
    spl_autoload_register(function ($c) use ($paths) {
    if (isset($paths[$c])) require $paths[$c];
    });
    // vs.
    spl_autoload_register(function ($c) {
    $path = str_replace(‘\\’, ‘/’, $class);
    if (file_exists($path)) require $path;
    });
    

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54. BAD
    GOOD
    Composer dumped autoloader
    (1 autoloader; fast lookup; no file_exists)
    

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55. Summary of Best Practices
    1. Don’t use include_once or require_once
    2. Use spl_autoload_register, not __autoload
    3. Don’t throw exceptions in autoloaders
    4. One class per file
    5. Namespaces/classes match directories/files
    6. Follow PSR-4 (or PSR-0)
    7. Use Composer, even if no dependencies
    8. Use classmap autoloaders in production
    

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56. Autoloading on Autopilot
    by Jeremy Lindblom (@jeremeamia)
    

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