Description:
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Casting large numbers to integers as array keys leads to unexpected results that are not obvious when looking at the code. It appears the 32-bit integer limit is being reached.

Casting the key to a string or triggering an error letting the user know something went wrong would be more helpful. 

I think it's much more useful to have the wrong type than the wrong value as the key. Additionally, casting to an integer has a chance to replace an existing key.

Releated bugs: 51430 shows as duplicate of 51008 which shows a status of Closed and says fixed.

Test script:
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$arr = [1410065407 => 'some value'];
$arr[9999999999] = 'another value';
var_dump($arr);


Expected result:
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array (size=2)
  1410065407 => string 'some value' (length=10)
  '9999999999' => string 'another value' (length=13)

Actual result:
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array (size=1)
  1410065407 => string 'another value' (length=13)