7.13. Creating a Class Dynamically7.13.1. ProblemYou want to create a class, but you don't know everything about it until your code is executed. 7.13.2. SolutionUse eval( ) with interpolated variables: eval("class van extends $parent_class { function van() { \$this->$parent_class(); } };"); $mystery_machine = new van; 7.13.3. DiscussionWhile it's okay in PHP to use variable names to call functions or create objects, it's not okay to define functions and classes in a similar manner: $van( ); // okay $van = new $parent_class // okay function $van( ) {}; // bad class $parent_class {}; // bad Trying to do either of the last two examples results in a parser error because PHP expects a string, and you supplied a variable. So, if you want to make a class named $van and you don't know beforehand what's going to be stored in $van, you need to employ eval( ) to do your dirty work: eval("class $van {};"); There is a performance hit whenever you call eval( ), so high traffic sites should try to restructure their code to avoid this technique when possible. Also, if you're defining your class based on input from users, be sure to escape any potentially dangerous characters. 7.13.4. See AlsoRecipe 7.14 to instantiate an object dynamically; documentation on eval( ) at http://www.php.net/eval. Copyright © 2003 O'Reilly & Associates. All rights reserved. |
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