Online PHP editor | output for 2hbc3

<?php function test($array) { try { return is_indexed_array($array); } catch (Exception $e) { echo $e->getMessage(); return 'error'; } } function is_indexed_array($array) { if (!is_array($array)) return false; foreach (array_keys($array) as $k => $v) if ($k !== $v) return false; return true; } // non-array - adjust according to your preferred error handling technique assert(test(null) === false); assert(test(false) === false); assert(test(new stdClass) === false); // empty array assert(test([]) === true); // numeric keys assert(test([null, 'a', 'b']) === true); // proper indexed array; also, to catch wrong isset usage assert(test([1 => 'a', 2 => 'b', 3 => 'c']) === false); // sequential but not 0-based assert(test([-1 => '', 0 => '', 1 => 'a']) === false); // sequential but not 0-based assert(test([0 => '', 2 => 'b', 3 => 'c']) === false); // 1 index missing assert(test([0 => '', 2 => 'b', 1 => 'a']) === false); // numeric but unordered assert(test([0 => '']) === true); // single item assert(test([1 => 'a']) === false); // single item assert(test([NAN]) === true); assert(test([NAN => '']) === false); assert(test([INF]) === true); assert(test([INF => '']) === false); // string keys assert(test(['' => '', 'a' => 'a', 'b' => 'b']) === false); // proper associative array assert(test(['' => '']) === false); // single item; also, associative even though '' == 0 // mixed keys assert(test(['' => '', 1 => 'a']) === false); // first key string but rest not assert(test(['' => '', 0 => '']) === false); // first key string but rest not assert(test([0 => '', 'a' => 'a']) === false); // first key numeric but rest not // numeric string keys assert(test([' 0' => '']) === false); // associative even though ' 0' == 0 assert(test(['00' => '']) === false); // associative even though '00' == 0 assert(test(['0*' => '']) === false); // associative even though '0*' == 0 assert(test(['0.0' => '']) === false); // associative even though '0.0' == 0.0 assert(test(['0x0' => '']) === false); // associative even though '0x0' == 0 assert(test(['0e0' => '']) === false); // associative even though '0e0' == 0 $obj = new stdClass; $obj->{0} = ''; assert(test((array)$obj) === false); // to catch ['0' => ''] like situations