Front page | perl.perl5.porters |
Postings from October 2015
On Mon, Oct 12, 2015 at 6:22 AM, Dave Mitchell <davem@iabyn.com> wrote:
> 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.
It doesn't matter what code it *results* in.
use constant FOO => $x;
when (FOO)
is no different than
when ($x)
and we all agree the latter is not workable. FOO is the still the result of
an arbitrary expression, even if the expression is evaluated at
compile-time. This differs from
when ("x")
when (4)
because that bases behaviour on the *source* code.
Thread Previous
|
Thread Next