[Vm-dev] Re: [Pharo-dev] thisContext usecases

[Eliot Miranda]

Hi Clément,

    this is a bug.  Thanks for finding it.

On Tue, Jul 9, 2013 at 1:15 AM, Clément Bera <bera.clement at gmail.com> wrote:

> Hello pharoers,
>
> Recently I have been looking at the Pharo thisContext capabilities, in
> order to perhaps one day in the far future edit its implementation with the
> Pharo dev team. Nothing is planned or confirmed, it is just to discuss.
>
> A context has instances variables (method closureOrNil
> receiver stackp sender pc) and holds the arguments and temporaries.
>
> Now I'd like to know what context's state do we modify, and what states
> are just internal representations ?
>
> For example, it seems that you can do 'thisContext receiver: #foo', but
> you cannot with Cog.
>
> SomeClass>>foo
> thisContext receiver: #foo.
>  ^ self
>
> In workspace, evaluating:
> 1 to: 5 do: [:i | Transcript show: SomeClass new foo ]
>
> Transcript result (with Cog):
> foo
> foo
> a SomeClass
> a SomeClass
> a SomeClass
>
> Transcript result (with Stack or Vanilla):
> foo
> foo
> foo
> foo
> foo
>
> Now as no one has ever complained, I guess this feature is not used.
>
> As far as I know, the real use cases of the context seems to be:
> - setting and gettings temporaries
> - setting and getting the sender of a context
> - setting and getting the pc
> - getting method, closureOrNil, receiver, stackp, arguments but NOT
> setting them
>
> Now setting the sender of a context seems to be used only in two cases:
> - continuations (as seaside continuations)
> - exception implementation
>
> So imagine that in the future you would have a context that can be
> accessed in read-only, where you could only:
> - set the temporaries (but not arguments)
> - set the pc (or something equivalent, as set the currently executed ast
> node)
> - use continuations (exceptions can be implemented on top of continuations)
>
> I would like to know if there are things that you do now and that you
> would not be able to do with a context like that. For non meta developer
> (like enterprise app developer) I guess it will not change anything, but I
> want to know if you implemented a framework as seaside, does it requires
> other things from the context and why ?
>
> Thanks for answering,
>



-- 
best,
Eliot
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