[bitc-dev] Semantics of unboxed
Jonathan S. Shapiro
shap at eros-os.org
Thu Oct 21 07:08:53 EDT 2004
This is not a semantics issue. I'm trying to stick to semantic concerns
for the moment.
On Wed, 2004-10-20 at 21:13, EricNorthup wrote:
> Shap wrote:
> > Consider two similar types.
> > (tuple-of int (tuple-of char float))
> > (tuple-of int (unboxed tuple-of char float))
> > So far as I can tell, there appears to be NO semantic difference to
> > these two things. In particular, the relationship between the inner
> > tuple and the outer tuple is 1:1 in both cases, and since our language
> > now allows obtaining a reference to a boxed thing in a fashion that
> > works just like a reference to an unboxed thing, it appears to me that
> > there are no statements that can differentiate the fact that the inner
> > tuple is boxed.
> There is perhaps one difference, which is not an issue of semantics but
> rather performance. Taking a reference to a boxed object never requires
> the (typeid, bits *) pointer form. So if we are going to be making lots
> of references to something, it might be desirable to leave it boxed.
> However this strikes me as a bit of a u-optimization, which is obviously
> less important than simplifying (and spec'ing + implementing!) the language.
> > If this is really correct, then we can omit all consideration of
> > "boxedness" from the language semantics...
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