Matt Fowles <[EMAIL PROTECTED]> wrote:
> Leo~
> On Sun, 27 Mar 2005 16:37:41 +0200, Leopold Toetsch <[EMAIL PROTECTED]> wrote:
>> 5) infix method signature change:
>>
>> METHOD PMC* add( [INTERP, SELF,] PMC* rhs, PMC ´*dest) {
>> if (!dest)
>> dest = pmc_new(INTERP, SELF->vtable->base_type);
>> ...
>> return dest;
>> }
>>
>> If the destination PMC is passed in, it's used else a new PMC of an
>> appropriate type is created.
> I would actually appreciate a refresher on the original motivation
> behind never autogenerating a LHS. I recall being told it has
> something to do with tied data, but I was never clear on exactly how
> that related.
I'd say: tied variables or references to variables:
$r = \$a;
$a = $a + 2;
If the add operation produced a new destination, the reference is lost.
> ... I would think that tied data would only require
> VTABLE_assign method, and would not care how its RHS was created (via
> an add or mul or whatever).
You can write it in both ways:
temp = a + 2
assign a, temp
or
a = a + 2 # current sematics, a modified in place
or with lexicals/globals:
a = find_lex "a" # or a = global "a"
a = a + 2
The final operation to assign the value to the perl var has IMHO always
to reuse the existing var.
> Thus I would argue for having most operators create their result (but
> having a special assign that would call a VTABLE method) and forcing
> languages with active data to go through a two step assignment
> $P0 = $P1 + $P2 # P0 created
> $P3 <- $P0 # P3 gets to run its tied code
We could do it that way too. OTOH it always needs two opcodes to
achieve the current effect of working with existing destination PMCs.
> and languages like python which have immutable scalars could always use
> $P0 = $P1 + $P2 # P0 created
As said, we can create either "__add" or "__n_add" depending on some
pragma or depending on the HLL.
> One concern that occurs to me is that this would cause more new PMC
> allocations. But I am whether or not that is true.
The C<temp> above isn't needed, so yes.
>> infix "__i_add", d, r
> I think this one is very necessary.
Yep
> Matt
leo
