Description:
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When use (array) to convert the object to array, the key will using string even the it is integer, then the string key will never been get.

Test script:
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$obj = '{"300": {"id": "foo"}}';
$obj = json_decode($obj);
$obj = (array)$obj;
var_dump($obj); // array (size=1) '300' => string 'foo' (length=3)
var_dump($obj["300"]); // null
var_dump($obj[300]); // null

Expected result:
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It should be convert the object key to integer if it can convert to integer.

Actual result:
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When convert the object the key will always be string even the key can convert to integer.