Dan Sugalski wrote:
> At 02:29 PM 9/29/00 +0100, David Mitchell wrote:
> >Regarding the tentative list of vtable functions:
> >I'm rather worried about binary operators, eg 'is_equal', 'add' etc.
> >The danger with these is that they may impose a single implementation
> >of scalars upon us.
> >
> >As an example, suppose I wrote an alternative scalar implementation that
> >was optimised for many small string appends followed by a single get
> >of the wholpe string at the end. (I might internally do this with a linked
> >list of blocks, say; then allocate a single large block at the end to
> >return the whole string.)
> >
> >If sv1 is a standard SV and sv2 is an append-optimised one, then
> >
> >(sv1->vtable[IS_EQUAL])(sv1,sv2) would crash and burn, because
> >sv1's 'is_equal' function doent know that sv2 has a different internal
> >representation.
>
> Your worries are well-founded, but ultimately not a problem. (I do like
> those kinds... :)
>
> Since the generic internal representation of a variable is hidden from
> anything but that variable's vtable, the scenario you propose can't happen.
> What'd happen instead for a plain ASCII string compare would look something
> like:
>
> bool is_equal(pmc1, pmc2) {
> if (strcmp(pmc1->string, to_string(ASCII, pmc2)) {
> return Perl_FALSE;
> } else {
> return Perl_TRUE;
> }
> }
>
> Overloading does present an ordering issue, and one I am worried about. It
> either requires all the vtable functions to know about all the variable
> types (which is impossible, unfortunately) or it means perl needs to
> dynamically reorder the operation so the 'bigger' variable's function gets
> called.
>
> Reordering's also not a 100% panacea--it's fine for ops involving a base
> type and an extended type, but it can potentially break down with two
> extended types. (What happens when you add a complex number with a complex
> bigint, if the two types have no idea about each other?)
I have been wondering why not write Perl in C++ from ground? Performance?
Portability?
In C, it takes alot of time to design vtable ,however still couldn't work
completely as OO.
If write in C++, the vtable will be generated during the compile phrase and
perfectly.
>
> Dan
>
> --------------------------------------"it's like this"-------------------
> Dan Sugalski even samurai
> [EMAIL PROTECTED] have teddy bears and even
> teddy bears get drunk
--
Sincerely,
Ye, Wei
