Reclassified as feature request.

The same issue is with NULL values;

$a = NULL;

echo $a['b'];

...and nothing happen

yeah, I remembered there was a similar bug report of this behavior, and I seems 
made a fix for it.

if I remember correctlly, it was merged into master-branch already

Bug still occurs on a 5.5-dev version.

example: http://codepad.viper-7.com/rn5kBm

Still exists in PHP 5.6:

$ php -d error_reporting=E_ALL -r '$x = false; var_dump($x[5]);'
NULL

Related: https://bugs.php.net/bug.php?id=39915

Also it silently returns NULL when trying to pass a number as an array: 

-------------

<?php
 
error_reporting(E_ALL);
$int = 1;
var_dump($int[100]);

-------------

Expected: Error using integer as array
Actual result: NULL

I thing using a scalar value as an array is obviously user's error and it should be reported, e.g. with error message.

Tested in PHP 5.6.7 (Debian), no error message reported. 

The same result if we use float instead of int. The same result if we use resource as array:

$ php -r 'error_reporting(-1);$h = fopen("/etc/passwd", "r"); $x = $h[0];var_dump($x);'
NULL

I attached a PR to this issue.  It attempts to only display an E_NOTICE once for extended failures like:

$a = false;
$a[1][2][3][4];

This should error once.  It will also raise an E_NOTICE for other FETCH_DIM_R opcodes like:

$a = false;
list($b, $c) = $a;

This would have 2 E_NOTICE one for each assignment to $b, and $c.

Will throw a notice in 7.4.

Trying to find RFC or PR or commit related to this bug...

- https://wiki.php.net/rfc/notice-for-non-valid-array-container
- from https://github.com/php/php-src/pull/2031#issuecomment-238315238