Description:
------------
As the following lines are ok:

$var = $var + 1;
$var[trim($var2)] = '';

I expected PHP to first evaluate the $key-String ([$var]), then modify $var. So a line like:

$var = 'a';
$var[$var] = 0;

should work. 

Reproduce code:
---------------
<?php
$var = 'xxxxx';
$var[$var] = true;
var_dump($var);
?>

Expected result:
----------------
array(1) { ["xxxxx"]=>  bool(true) }

or a warning like:
Warning: Cannot use a scalar value as an array 

Actual result:
--------------
string(5) "1xxxx"

Depending on what code was before it, or what was in $var before, the first character is not always '1'.