Description:
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As described in
http://php.net/manual/en/language.types.array.php
"Floats in key are truncated to integer."

This is somewhat unintuitive, and caught me the first time I met it. A PHP bug search shows me that other people were surprised too.

So to be kind to the programmers, also the ones who doesn't know the manual by heart, I would like to suggest that an E_STRICT error or similar be raised when the truncation is done.

Reproduce code:
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error_reporting(E_ALL | E_STRICT);

$x = 1.6;
$y = 1.7;
$a = Array();

$a[$x] = 1;
$a[$y] = 2;

echo $a[$x];


Expected result:
----------------
It prints out "2" in accordance with the manual

An E_STRICT is raised, as you are trying to use floats in a place where they do not belong. The E_STRICT error should recommend an explicit cast to int in the code.

Actual result:
--------------
It prints out "2" in accordance with the manual

No E_STRICT error is raised.