Language: object used as array key accepted — Zend TypeError Illegal offset type (zend_execute.c / zend_hash.c) #29532

Category

language · php-src-strict · array offset / hash key · pillar 4

Problem

Using an object as an array key must throw TypeError: Illegal offset type (objects are never valid hash keys; __toString is not consulted). VM/JIT accept the write: with a Stringable object the key becomes '' (empty string) after a failed/ignored conversion path; without __toString the write still succeeds and AFTER runs.

Probed 2026-08-09 @ 95c9b7659b vs Zend 8.2.32. JIT matches VM.

php-src reference

• php/php-src Zend/zend_execute.c — dimension write / illegal offset
• php/php-src Zend/zend_hash.c — zend_hash_* key type checks (Illegal offset type)
• Related closed (different surfaces): Regression: string offset with string/object/array dim — no TypeError, coerces (Zend/zend_execute.c) #22895 (string offsets), Stdlib: iterator_to_array() accepts array keys as "Array" — Zend TypeError Illegal offset type (ext/spl/iterator.c) #23573 (iterator_to_array), Language: array-literal enum case keys TypeError still "Illegal offset type" — Zend "Cannot access offset of type E" (Zend/zend_hash.c) #28628 (enum keys message)

PHP implementation target

• VM + JIT array dim write/fetch: reject IS_OBJECT keys with TypeError: Illegal offset type before any __toString coercion
• Prefer PHP-in-PHP in lib/VM / lib/JIT offset helpers; no new runtime/*.c

Repro

./script/docker-exec.sh -- bash -lc 'cat > /tmp/obj_key.php <<'"'"'PHP'"'"'
<?php
error_reporting(E_ALL);
class T {}
$a = [];
try {
  $a[new T()] = 1;
  echo "AFTER\n";
} catch (Throwable $e) {
  echo get_class($e), ": ", $e->getMessage(), "\n";
}
echo "done\n";
PHP
php /tmp/obj_key.php
php bin/vm.php /tmp/obj_key.php
php bin/jit.php /tmp/obj_key.php'

Done when

• VM + JIT: object as array key throws TypeError: Illegal offset type like Zend (with or without __toString)
• __toString is not invoked for array-key conversion
• Compliance/.phpt or test/repro/ guard
• php-src-strict; no php-compiler-strict shortcut