php-doc-en/language/oop5/autoload.xml

<?xml version="1.0" encoding="utf-8"?>
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 <sect1 xml:id="language.oop5.autoload" xmlns="http://docbook.org/ns/docbook">
  <title>Autoloading Classes</title>
  <para>
   Many developers writing object-oriented applications create
   one PHP source file per class definition. One of the biggest
   annoyances is having to write a long list of needed includes
   at the beginning of each script (one for each class).
  </para>
  <para>
   In PHP 5, this is no longer necessary. You may define an
   <function>__autoload</function> function which is automatically
   called in case you are trying to use a class/interface which hasn't been
   defined yet. By calling this function the scripting engine is given
   a last chance to load the class before PHP fails with an error.
  </para>
  <tip>
   <para>
    <function>spl_autoload_register</function> provides a more flexible
    alternative for autoloading classes. For this reason, using
    <function>__autoload</function> is discouraged and may be deprecated or
    removed in the future.
   </para>
  </tip>
  <note>
   <para>
    Prior to 5.3.0, exceptions thrown in the __autoload function could not be
    caught in the <link linkend="language.exceptions">catch</link> block and
    would result in a fatal error. From 5.3.0+ exceptions thrown in the
    __autoload function can be caught in the <link linkend="language.exceptions">
    catch</link> block, with 1 provision. If throwing a custom exception, then
    the custom exception class must be available. The __autoload function may
    be used recursively to autoload the custom exception class.
   </para>
  </note>
  <note>
   <para>
    Autoloading is not available if using PHP in CLI
    <link linkend="features.commandline">interactive mode</link>.
   </para>
  </note>
  <note>
   <para>
    If the class name is used e.g. in <function>call_user_func</function> then
    it can contain some dangerous characters such as <literal>../</literal>.
    It is recommended to not use the user-input in such functions or at least
    verify the input in <function>__autoload</function>.
   </para>
  </note>
  <para>
   <example>
    <title>Autoload example</title>
    <para>
     This example attempts to load the classes <literal>MyClass1</literal>
     and <literal>MyClass2</literal> from the files <filename>MyClass1.php</filename>
     and <filename>MyClass2.php</filename> respectively.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
function __autoload($class_name) {
    include $class_name . '.php';
}

$obj  = new MyClass1();
$obj2 = new MyClass2(); 
?>
]]>
    </programlisting>
   </example>
   <example>
    <title>Autoload other example</title>
    <para>
     This example attempts to load the interface <literal>ITest</literal>.
    </para>
    <programlisting role="php">
<![CDATA[
<?php

function __autoload($name) {
    var_dump($name);
}

class Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>
]]>
    </programlisting>
   </example>
   <example>
    <title>Autoloading with exception handling for 5.3.0+</title>
    <para>
     This example throws an exception and demonstrates the try/catch block.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
function __autoload($name) {
    echo "Want to load $name.\n";
    throw new Exception("Unable to load $name.");
}

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Want to load NonLoadableClass.
Unable to load NonLoadableClass.
]]>
    </screen>
   </example>
   <example>
    <title>Autoloading with exception handling for 5.3.0+ - Missing custom exception</title>
    <para>
     This example throws an exception for a non-loadable, custom exception.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
function __autoload($name) {
    echo "Want to load $name.\n";
    throw new MissingException("Unable to load $name.");
}

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Want to load NonLoadableClass.
Want to load MissingException.

Fatal error: Class 'MissingException' not found in testMissingException.php on line 4
]]>
    </screen>
   </example>
  </para>

  <simplesect role="seealso">
   &reftitle.seealso;
   <para>
    <simplelist>
     <member><function>unserialize</function></member>
     <member><link linkend="unserialize-callback-func">unserialize_callback_func</link></member>
     <member><function>spl_autoload</function></member>
     <member><function>spl_autoload_register</function></member>
    </simplelist>
   </para>
  </simplesect>

 </sect1>
 
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