Why does this set $this->object to a different instance (the one from the constant pool)?

@chitoku-k
Because $this->object may be a string (on PHP type) or an other object.
$this->object allows being a dynamic generated object, not just a reference to the Constant Pool.

For the above reasons, if the code substitutes a value to $this->object, the $this->object ensures the Constant Pool entry string data. (In this case, it ensures a _Utf8 structure.)

Herewith, if operand stack is stacking _String object, but operations can be proceeded correctly.

Thanks for your answer but it still does not seem to answer my question, in other words, why does it need to set it?

Finally, it turned out that $this->object must be equal to the instance already existing in the constant pool because any later comparison might not be guaranteed to treat them equal (such as if_a operation). Although it somewhat looks like String#intern() is affected by the internal object in the constant pool, this implementation is actually derived from the restriction of the way _Utf8 and _String relate to each other.