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<?php class x { public $a = [ '~.~' => '$this->waa($0);' ]; function p($s) { foreach($this->a as $p => $r) { $s = preg_replace_callback($p, function($m) use ($s, $r){ $c = preg_replace('~\$(\d)~', '$m[$1]', $r); print "\n$c\n"; return eval($c); }, $s); } return $s; } function waa($t){ return '*'.$t.'*'; } } var_dump((new x)->p('wazup'));
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 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 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
$this->waa($m[0]); $this->waa($m[0]); $this->waa($m[0]); $this->waa($m[0]); $this->waa($m[0]); string(0) ""

preferences:
236.17 ms | 404 KiB | 326 Q