(Sorry for the delay of response, I am currently in a remote area.)
> Le 6 juil. 2014 à 20:15, André Bargull <[email protected]> a écrit :
>
>
>> Moreover, the Completion record (either normal or abrupt) returned
>> from [[Call]] will hold an additional [[thisValue]] field,
>> which, unless otherwise specified:
>>
>> * is set to the original `thisArgument` if it was not empty; or,
>> * is set to the value (at the time of completion) of the this-binding,
>> if it was initially uninitialised but has been initialised; or,
>> * is absent if the this-binding was left uninitialised.
>
> Hmm, mixed feelings about extending the Completion record type to hold
> another field. It could be problematic for implementors to store this
> additional state efficiently. On second thought, it should be possible to
> merge [[thisValue]] with the existing [[Value]] field, and conditionally
> handle [[Value]] == empty in [[Construct]]? [1]
An issue here is that I want to initialise the this-binding of the caller even
when the callee ends abruptly (with `throw`).
>
>
>> Moreover, the Completion record (either normal or abrupt) returned
>> from [[Call]] will hold an additional [[thisValue]] field,
>> which, unless otherwise specified:
>>
>> * is set to the original `thisArgument` if it was not empty; or,
>> * is set to the value (at the time of completion) of the this-binding,
>> if it was initially uninitialised but has been initialised; or,
>> * is absent if the this-binding was left uninitialised.
>
> Tail-call semantics may interfere with determining the value of "this-binding
> at the time of completion", because the execution context was already popped
> from the stack at that time. Probably solvable by determining the
> this-binding before performing the tail-call, plus some special casing when
> the tail-call expression is a super-call.
>
>
>> --------------------------------
>>
>> When, say, `super.method(..args)` is called, the following steps are taken:
>>
>> 1. Let `F` be the method referenced by `super.method`.
>
> This part needs to be redefined. `super.method` is an abbreviation for:
>
> 1. Let env be GetThisEnvironment().
> 2. Let baseValue be GetSuperBase(env).
> 3. Let actualThis be GetThisBinding().
> 4. Let result be baseValue.[[Get]]("method", actualThis).
>
> But at `this`-binding initialisation time, `actualThis` is still the empty
> placeholder object, so it cannot be used as the receiver argument for the
> [[Get]] internal method call.
>
>
> [1] https://gist.github.com/anba/e6b525c124d09dafaed6
Here is another setting that I've thought of: When `super` is called with a
not-yet-initialised this-binding, the this-binding of the callee is in fact a
special pointer to the function environment record of the caller, and when the
callee wants to read or update it's this-binding, it reads or update the one of
the caller.
—Claude
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