On Mon, Oct 23, 2000 at 08:27:52PM -0400, Dan Sugalski wrote:
> At 12:33 AM 10/24/00 +0100, Simon Cozens wrote:
> >On Mon, Oct 23, 2000 at 03:40:26PM -0700, Peter Scott wrote:
> > > >Don't forget that those BEGIN blocks are *supposed* to be instructions
> > > >to the compiler.
> > >
> > > Er, but a lot of people seem to use them for other things :-)
cos perl 5.004 or so didn't have INIT blocks and so BEGIN is doing 2 jobs:
hints & instructions to the parser & compiler, and run time initialisation.
> A lot of the tiny programs aren't all that tiny, either. Ten lines isn't
> much unless one of them's "use CGI;" or "use Net::FTP". And there are huge
> gobs of those.
while use ...; maps to
BEGIN {
require ...;
}
we still potentially have both compiler (directives & declarations) and
run time (initialisation) in the one place. perl 6 module writers will
have to get good at putting blocks of module inside INIT blocks.
Maybe the perl5 to perl6 convertor will be taking a module that looks like
this
package locale;
$locale::hint_bits = 0x800;
sub import {
$^H |= $locale::hint_bits;
}
sub unimport {
$^H &= ~$locale::hint_bits;
}
1;
and turning them into:
package locale;
our $locale::hint_bits;
INIT {
$locale::hint_bits = 0x800;
}
sub import {
$^H |= $locale::hint_bits;
}
sub unimport {
$^H &= ~$locale::hint_bits;
}
so that definitions and declarations are still BEGIN time (which happens
once in a program's life when it gets compiled), but initialisations are
moved to INIT time (which happens 0 to lots of times; ie once per running)
Hmm. I was about to say "Except that maybe that should be:
our $locale::hint_bits = 0x800;
" but I think not; even in perl5 it doesn't get initialised until the
code runs when the scope ends at the "1;" Modules that did
BEGIN {$locale::hint_bits = 0x800;}
still do what's expected of perl5 when written:
INIT {
BEGIN {$locale::hint_bits = 0x800;}
}
Nicholas Clark
