Online PHP editor | output for JJSvR

<?php function do_split($name) { return preg_split('/([A-Z]{2,}|([A-Z][^A-Z]*))/', $name, null, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY); } function convert_case($name) { return implode( '_', array_map( 'strtolower', do_split($name) ) ); } function convert_case2($in) { $len = strlen($in); if ($len < 2) { return strtolower($in); } // no state $upper = function ($c) { return 'A' <= $c && $c <= 'Z'; }; $lower = function ($c) { return 'a' <= $c && $c <= 'z'; }; $alpha = function ($c) use ($upper, $lower) { return $upper($c) || $lower($c); }; $num = function ($c) { return '0' <= $c && $c <= '9'; }; $alpha_num = function ($c) use ($alpha, $num) { return $alpha($c) || $num($c); }; // stream state $pos = 0; $char = $in[0]; $peek = function() use ($in, &$pos, $len) { if ($pos+1 >= $len) { return null; } return $in[$pos+1]; }; $next = function() use ($peek, &$pos, &$char) { $char = $peek(); $pos++; return $char !== null; }; // lex state $out = array(); $upper_word = null; $lower_word = null; $cap_word = null; $num_word = null; $find_word = function () use (&$char, $alpha_num, $lower, $upper, $next, $peek, &$lower_word, &$upper_word, &$cap_word, &$num_word) { while (!$alpha_num($char)) { if (!$next()) { return null; } } if ($lower($char)) { return $lower_word; } if ($upper($char)) { if ($upper($peek())) { // uppercase word return $upper_word; } return $cap_word; // capitalized word } return $num_word; }; $upper_word = function() use (&$out, &$char, $next, $peek, $upper, $lower, $find_word) { $word = $char; while ($next() && $upper($char)) { if ($lower($peek())) { // start of capitalized word (e.g. FOOBar at B) break; } $word .= $char; } $out[] = $word; return $find_word; }; $lower_word = function() use (&$out, &$char, $next, $lower, $find_word) { $word = $char; while ($next() && $lower($char)) { $word .= $char; } $out[] = $word; return $find_word; }; $cap_word = $lower_word; $state = $find_word; while ($state !== null) { $state = $state(); } return strtolower(implode('_', $out)); } convert_case2('FooBARbar0123'); $samples = array( 'FooBar', 'FooBAR', 'FOOBar', 'foo_bar', 'FOO_bar', 'FOO_Bar', 'foo_BAR', 'foo_Bar', 'Foo_bar', ); print_r(array_map(function ($name) { return array( 'name' => $name, 'converted' => convert_case2($name), // 'converted' => convert_case($name), ); }, $samples));