Description:
------------
After manipulating arrays using [] or creating an array in the form array("key" => value, ...) or calling unset on an array element. json_encode will encode the array as an object rather than an array.

Reproduce code:
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echo json_encode(array(1 => new stdClass(), 2 => new stdClass(), 3 => new stdClass()));
$m = array();
$m[1] = new stdClass();
$m[2] = new stdClass();
$m[3] = new stdClass();
echo json_encode($m);
$m = array_values($m);
echo json_encode($m);
unset($m[0]);
echo json_encode((array) $m);


Expected result:
----------------
["1":{},"2":{},"3":{}]
["1":{},"2":{},"3":{}]
[{},{},{}]
["1":{},"2":{}]

Actual result:
--------------
{"1":{},"2":{},"3":{}}
{"1":{},"2":{},"3":{}}
[{},{},{}]
{"1":{},"2":{}}