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run code in 300+ PHP versions simultaneously
<?php $foo = 'foo'; var_dump(memory_get_usage()); foreach (range(1,100) as $i) { $$i = $foo; } var_dump(memory_get_usage()); foreach (range(1,100) as $y) { $$y &= $foo; } var_dump(memory_get_usage());

preferences:
29.93 ms | 402 KiB | 5 Q