Files should either execute code or declare new structures (classes, interfaces, functions, etc.) but shouldn't do both.
Declaration files will be included at some point in the code, so as to provide the necessary definitions to run a script. They shouldn't have other effect than providing a definition. Any other side effect may interfere with the running code, which should be left as main commander.
This rule require that files contains only definitions for functions, constants, classes, traits or interfaces. A few exceptions may apply to conditional definition, and direct access prevention.
The following patterns are considered warnings:
<?php
class x { /**/ }
// main script should initialize that variable only if needed
if (x::staticProperty === null) {
$main_variable = new x();
}
?>The following code is considered legit :
<?php
// direct access
if (!defined('APP_CONSTANT')) { die(); }
// conditional declarations
if (defined('APP_CONFIGURATION')) {
class x { /**/ }
} else {
class x { /**/ }
}
?>