7.13. Instantiating an Object Dynamically
Problem
You want to instantiate an object, but you don’t know the name of the class until your code is executed. For example, you want to localize your site by creating an object belonging to a specific language. However, until the page is requested, you don’t know which language to select.
Solution
Use a variable for your class name:
$language = $_REQUEST['language']; $valid_langs = array('en_US' => 'US English', 'en_GB' => 'British English', 'es_US' => 'US Spanish', 'fr_CA' => 'Canadian French'); if (isset($valid_langs[$language]) && class_exists($language)) { $lang = new $language; }
Discussion
Sometimes you may not know the class name you want to instantiate at
runtime, but you know part of it. For instance, to provide your class
hierarchy a pseudo-namespace, you may prefix a leading series of
characters in front of all class names; this is why we often use
pc_
to represent PHP Cookbook
or PEAR uses Net_
before all Networking classes.
However, while this is legal PHP:
$class_name = 'Net_Ping'; $class = new $class_name; // new Net_Ping
This is not:
$partial_class_name = 'Ping'; $class = new "Net_$partial_class_name"; // new Net_Ping
This, however, is okay:
$partial_class_name = 'Ping'; $class_prefix = 'Net_'; $class_name = "$class_prefix$partial_class_name"; $class = new $class_name; // new Net_Ping
So, you can’t instantiate an object when its class name is defined using variable concatenation in the same step. However, because you can use simple ...
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