Re: JavaMemberNode optimisation

On Mon, Dec 13, 2010 at 5:39 AM, Kevin Reid <kpreid-M/[email protected]> wrote:

> On Dec 13, 2010, at 5:58, Thomas Leonard wrote:
>
> > This change caused a slight side-effect: causeway does this:
> >
> >  def editorShellListener :ShellListener := def _ { ... }
> >
> >  editorShell.addShellListener(editorShellListener)
> >  ...
> >  editorShell.removeShellListener(editorShellListener)
> >
> > This relies on editorShellListener being the same (deflector) object
> > each time. However, E.as always unwraps the deflector and creates a
> > new
> > one.
>
>
> (Note that as a general invariant, it must be impossible to
> distinguish between objects which are considered the same by
> Equalizer. Deflectors and resolved promises are both wrappers that can
> cause trouble in these cases.)
>
> Merely avoiding making a new deflector would still result in this
> being a problem:
>
>  def editorShellListener := def _ { ... }
>  editorShell.addShellListener(editorShellListener :ShellListener)
>  editorShell.removeShellListener(editorShellListener :ShellListener)
>
> since a deflector is constructed twice.
>
> The fix which comes to mind is to use a weak table to ensure that
> there is at most one deflector for each combination of E-object and
> Java interface.
>

I like the weak table idea. The resulting system has strictly less odd
semantics than any of the alternatives.



>
> Or, we could make Deflectors not considered E-same as their referents;
> this would be safe since it happens at the moment of explicit
> coercion, but less transparent.
>
> --
> Kevin Reid                                  <http://switchb.org/kpreid/>
>
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>



-- 
    Cheers,
    --MarkM

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