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

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 <sect1 xml:id="language.oop5.iterations" xmlns="http://docbook.org/ns/docbook">
  <title>Object Iteration</title>
  <para>

   PHP provides a way for objects to be defined so it is possible to iterate
   through a list of items, with, for example a &foreach; statement. By default,
   all <link linkend="language.oop5.visibility">visible</link> properties will be used
   for the iteration.

  </para>

  <example>
   <title>Simple Object Iteration</title>
   <programlisting role="php">
<![CDATA[
<?php
class MyClass
{
    public $var1 = 'value 1';
    public $var2 = 'value 2';
    public $var3 = 'value 3';

    protected $protected = 'protected var';
    private   $private   = 'private var';

    function iterateVisible() {
       echo "MyClass::iterateVisible:\n";
       foreach ($this as $key => $value) {
           print "$key => $value\n";
       }
    }
}

$class = new MyClass();

foreach($class as $key => $value) {
    print "$key => $value\n";
}
echo "\n";


$class->iterateVisible();

?>
]]>
   </programlisting>
   &example.outputs; 
   <screen role="php">
<![CDATA[
var1 => value 1
var2 => value 2
var3 => value 3

MyClass::iterateVisible:
var1 => value 1
var2 => value 2
var3 => value 3
protected => protected var
private => private var
]]>
   </screen>

  </example>

 <para>
  As the output shows, the &foreach; iterated through all of the
  <link linkend="language.oop5.visibility">visible</link> properties that could be
  accessed.
 </para>

 <simplesect role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="language.generators">Generators</link></member>
    <member><interfacename>Iterator</interfacename></member>
    <member><interfacename>IteratorAggregate</interfacename> </member>
    <member><link linkend="spl.iterators">SPL Iterators</link></member>
   </simplelist>
  </para>
 </simplesect>

 </sect1>
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