Edwin Steiner wrote:
>
> Dan Sugalski wrote:
> [snip]
> > That's OK, since my example was wrong. (D'oh! Chalk it up to remnants of
> > the martian death flu, along with too much blood in my caffeine stream) The
> > example
> >
> > $foo{bar} = $baz + $xyzzy[42];
> >
> > turns into
> >
> > baz->vtable->add[NATIVE](foo, baz, xyzzy, key);
>
> Why does the bytecode compiler know it should generate NATIVE int addition?
> Are you assuming 'use integer'? (see also next comment)
[snip]
I thought about it once more. Maybe I was confused by the *constant* NATIVE.
Are you suggesting a kind of multiple dispatch (first operand selects
the vtable, second operand selects the slot in the vtable)?
So
$dest = $first + $second
becomes
first->vtable->add[second->vtable->type(second)](dest,first,second,key);
?
or maybe
first->vtable->add[second->vtable->slot_select](dest,first,second,key);
which saves a call by directly reading an integer from the vtable of <second>.
(BTW, this is also how overloading with respect to the second argument
could be handled (should it be decided on the language level to do that):
There could be a slot like add[ARCANE_MAGIC] selected by
second->vtable->slot_select
which does all kinds of complicated checks and branches without any cost
for the vfunctions in the other slots.)
Such a multiple dispatch seems to me like the only solution which avoids
the following (eg. in Python):
'first + second' becomes
1. call virtual function 'add' on <first>
2. inside first->add do lots of checks about type of <second>
-Edwin
