3v4l.org

run code in 300+ PHP versions simultaneously
<?php class test { function register() { if (!function_exists('test_init')) { function test_init() { echo 'Initializing library'.PHP_EOL; } } } } $test = new test; $test->register(); test_init(); ?>
Output for 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.38, 7.0.0 - 7.0.33, 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.31, 8.2.0 - 8.2.26, 8.3.0 - 8.3.15, 8.4.1 - 8.4.2
Initializing library
preferences:
94.19 ms | 408 KiB | 5 Q