Description:
------------
PHP doesn't output any warning for $a['zz'] if $a is not an assoc array.
This problem has been reported in Bug #33879 in the particular case where $a is a string. Since individual chars in a string can be accessed using the $a[] syntax, and since the key 'zz' will be automatically cast to 0, then I can understand why PHP will accept $a['zz'] without complaining.
But when $a is an integer, or a bool, or anything else that has nothing to do with an array (or a string), I don't see any reason why PHP should accept $a['zz'] without complaining! It would make some bugs much easier to find...

Reproduce code:
---------------
<?php
error_reporting(E_ALL);

$assoc = array();
$test = $assoc['zz']; // Warning "Undefined index: zz..." issued. OK

// Now what if the $assoc variable is replaced by a variable that is not
// an assoc array?
// The expected/natural behaviour would be that PHP complains even
// stronger because if such situation were occuring with a compiled
// language, any descent compiler would not even compile.

$not_an_assoc = 85;
$test = $not_an_assoc['zz']; // No warning issued!
echo gettype($test); // -> Display NULL

$not_an_assoc = "85";
$test = $not_an_assoc['zz']; // No warning issued!
echo $test; // -> Display 8
?>

Expected result:
----------------
It would be nice if PHP could tell me I'm doing something wrong with a warning or an error (that's why I'm using error_reporting(E_ALL) after all).