isset() And The Fatal Error¶

<?php

$a = [];
$a['b']['c']['d'] = 1;
$a['b']['c']['d2'] = new stdclass();
$a['b']['c']['d3'] = [];

var_dump(isset($a['b']['c']['d'])); // as expected, and within type
var_dump(isset($a['b']['c']['f'])); // as expected, and within type

var_dump(isset($a['b']['c']['d']['g']));   // as expected, because 'd' is 1
var_dump(isset($a['b']['c']['d']->g));     // as expected, because 'd' is 1

var_dump(isset($a['b']['c']['d3']->f));    // as expected, because 'd' is an array
var_dump(isset($a['b']['c']['d3']['f']));  // as expected, because 'd' is an array

var_dump(isset($a['b']['c']['d2']->f));   // as expected, because 'd' is an object
var_dump(isset($a['b']['c']['d2']['f']));   // fatal error!!

var_dump(isset($a['b']['c']['D']['g']->f));   // as expected, because 'D' is actually null
var_dump(isset($a['b']['c']['D']['g']['f'])); // as expected, because 'D' is actually null

// isset($a['b']['c']['d']) is set so following are true and within type
var_dump(isset($a['b']['c']));
var_dump(isset($a['b']));

$i = 1;
echo $i[3]; // error,

isset() checks if a variable exists. By extension, it also checks array elements, object properties etc. As the check is performed, any attempt to access an undefined part of the expression is muted: this makes total sense.

For example, if one of the intermediate expression is an integer, it is not possible to access it with an array syntax, unlike an array or a string. Such access is a warning when used outside isset(), but is silent inside the isset().

This leads to a nice optimisation, where checking isset($a[1][2][3][4]) is sufficient to check isset($a), then isset($a[1]), isset($a[1][2]), isset($a[1][2][3]), and isset($a[1][2][3][4]). Nice.

The catch is when of the element inside the actual array is an object. PHP reports a fatal error when using an object with an array syntax (except may be for ArrayAccess objects). Then, isset() stops.

The reverse is not true: accessing an array with a object syntax yields a null and no warning. As it should be.

All this also applies to empty().

A change of behavior was suggested for PHP 8.5, but was down voted. May be in PHP 8.6?

PHP Error Messages¶

Cannot use object of type stdClass as array

PHP Features¶

Last updated: 14 July 2026

isset() And The Fatal Error¶

See Also¶

PHP Error Messages¶

PHP Features¶