Description:
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By default (for some reason) SPL's ArrayObject does not allow accessing members like object properties. In order to enable this behavior you must use the **UNDOCUMENTED** technique of `$arrayobject = new ArrayObject($array, ArrayObject::ARRAY_AS_PROPS);`.

However this setting is not saved during serialization, so when unserializing the ArrayObject it reverts to it's default behavior (throwing errors when trying to perform a `$arrayobject->key;`).

I believe given that since this is a mapping of an array to an object (and not arrayaccess), ARRAY_AS_PROPS should be default behavior.

However, if one is paranoid about BC breaks, at least update ArrayObject to store the ARRAY_AS_PROPS flag to support serialization.

Reproduce code:
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<?php
$arrayobject = new ArrayObject(array('key'=>'value'), ArrayObject::ARRAY_AS_PROPS);

echo $arrayobject->key;

$arrayobject = serialize($arrayobject);
$arrayobject = unserialize($arrayobject);

echo $arrayobject->key;

Expected result:
----------------
'value'
'value'

Actual result:
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An error is raise on the last line trying to access a nonexistant property.