9.1.2 [[SetPrototypeOf]] (V)

While reading the SetPrototypeOf algorithm I noticed that some steps are
repeated. At step 5, if O.[[Extensible]] is false, the method returns
false. But at step 8, the same condition is checked again. It seems to me
that between these steps neither the value of O, nor the value of
O.[[Extensible]] changes. Aren't steps 7 and 8 redundant?
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On Mon, Jun 30, 2014 at 10:18 AM, raul mihaila <raul.mihaila at gmail.com>
wrote:

> While reading the SetPrototypeOf algorithm I noticed that some steps are
> repeated. At step 5, if O.[[Extensible]] is false, the method returns
> false. But at step 8, the same condition is checked again. It seems to me
> that between these steps neither the value of O, nor the value of
> O.[[Extensible]] changes. Aren't steps 7 and 8 redundant?
>

The second set of checks is needed because step 6 might change the results:
if one of the objects iterated over in step 6 is a proxy, then arbitrary
code can be executed through an invocation of its `getPrototypeOf` handler.
This code might make O inextensible or change its __proto__ to be the same
value as V.
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