Front page | perl.perl5.porters |
Postings from October 2015
On Wed, Oct 07, 2015 at 03:57:26PM -0400, Eric Brine wrote:
> On Wed, Oct 7, 2015 at 4:24 AM, Dave Mitchell <davem@iabyn.com> wrote:
>
> > 2. Make when's behaviour entirely dependent on the *compile-time* class
> > of of its arg. In particular, make 'when (FOO)' have exactly the following
> > behaviours:
> >
> > FOO condition evaluates to
> > -------------- ----------------------
> > literal undef !defined($_)
> > numeric const $_ == FOO
> > literal pattern $_ ~= FOO
> > all else $_ eq FOO
> >
> > 3. when { FOO } has condition FOO.
> >
> > For example:
> >
> > use constant ME => "davem";
> > when (ANS) # equivalent to when { $_ == 42 }
> >
>
> According to your table, shouldn't that be "when { $_ eq ANS }"? ANS could
> have any value, so when (ANS)" is no different than "when ($x)". There's no
> "compile-time class" available to study.
No, its specifically if FOO is a compile-time constant. At compile time
there is no difference between
when(42)
and
use constant FOO;
when(FOO);
They have both been compiled to a single OP_CONST with a constant SV
attached that can be examined at compile-time for numness. Of course,
sub FOO {}
when (FOO)
would be treated as ($_ eq FOO) still.
--
"Strange women lying in ponds distributing swords is no basis for a system
of government. Supreme executive power derives from a mandate from the
masses, not from some farcical aquatic ceremony."
-- Dennis, "Monty Python and the Holy Grail"
Thread Previous
|
Thread Next