On Tue, Dec 16, 2003 at 07:05:19AM -0700, Luke Palmer wrote:
: Michael Lazzaro writes:
: >
: > On Sunday, December 14, 2003, at 06:14 PM, Larry Wall wrote:
: > >But the agreement could be implied by silence. If, by the time the
: > >entire program is parsed, nobody has said they want to extend an
: > >interface, then the interface can be considered closed. In other
: > >words, if you think you *might* want to extend an interface at run
: > >time, you'd better say so at compile time somehow. I think that's
: > >about as far as we can push it in the "final" direction.
: >
: > That seems a very fair rule, especially if it adds a smidge more speed.
: > Runtime extension will likely be very unusual
:
: Unless you're me. Or Damian. Or a fair number of other programmers who
: like to dive into the Perl Dark Side on a regular basis.
:
: > -- requiring it to be explicit seems reasonable.
:
: It seems so. Knowing Larry, I'm sure this is an ungrounded fear, but I
: definitely want to be able to declare in a module "I'm going to be
: screwing with stuff; keep out of my way," so that I don't impose any
: awkward declarations on my module users. If that request can be made
: more explicit in the cases where that's possible, great, but the general
: declaration should be available.
Okay, we'll call the general declaration:
use $&
or some such. :-)
Seriously, I hope we can provide a framework in which you can screw
around to your heart's content while modules are being compiled,
and to a lesser extent after compilation. But we'll never get to a
programming-in-the-large model if we can't limit most of the screwing
around to the lexical scope currently being compiled, or at least
to a known subset of the code. Modules that turn off optimization
for all other modules are going to be about as popular as $&. So
the general declaration should probably be something easy to see like:
use STRANGE_SEMANTICS_THAT_SLOW_EVERYONE_DOWN;
That will encourage people to be more specific about what they want
to pessimize. Certainly, your fancy module should be encouraged
to declare these things on behalf of its users if it can. I'm not
suggesting that Lukian or Damianly modules force such declarations onto
the users unless it's impossible for the module to know. And it seems
to me that with sufficient control over the user's grammar, you can
often get that information into your own fancy module somehow.
Might take a few macros though, or analysis of the user's code at
CHECK time (or maybe just before).
And in general, it's probably not necessary to declare all the new
interfaces, but only those interfaces known at compile time that want
to stay open. Any interfaces added at run time are probably assumed
to be open. So in some cases you might find yourself deriving a
single open class at compile time from which you can derive other
open classes later.
But still, the principle remains that original declarer of an
interface doesn't know in general whether its users are going to want
to extend it. At some point the users have to take responsibility
if they want their code to run fast. Or run at all...
So we need to make it very easy for users to provide this kind of
information when it's needed.
Larry
