Front page | perl.perl5.porters |
Postings from December 2010
On 12 December 2010 21:26, Father Chrysostomos
<perlbug-followup@perl.org> wrote:
> # New Ticket Created by Father Chrysostomos
> # Please include the string: [perl #80628]
> # in the subject line of all future correspondence about this issue.
> # <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=80628 >
>
>
> This patch adds a __SUB__ keyword that returns the current subroutine, or undef for the main program, a special block, or an eval.
>
> If there are no objections, I will add docs and push this shortly before 5.13.8.
>
> I first thought of adding this to make recursive lexicals subs easier to write (whenever they are added):
>
> my sub foo { __SUB__->() }
>
> my sub foo; # the alternative
> my sub foo { foo() }
>
>
> The really neat thing, which I realised only after writing it, is that it allows for recursive closures to be written much more simply:
>
> sub make_recursive_function {
> my $arg = shift;
> sub {
> print "$_[0]\n";
> __SUB__->($_[0] + 1) if $_[0] < $arg;
> }
> }
>
> as opposed to:
>
> use Scalar::Util;
> sub make_recursive_function {
> my $arg = shift;
> my $sub;
> my $life_raft = $sub = sub {
> print "$_[0]\n";
> &$sub($_[0] + 1) if $_[0] < $arg;
> }
> Scalar::Util::weaken($sub);
> $sub;
> }
And this demonstrates why the patch would be useful.
Even FC got the recipe wrong. :-)
It should return $life_raft, not $sub, otherwise $sub will be a "dead
weakref", and the sub freed by the time this code exits.
cheers,
Yves
--
perl -Mre=debug -e "/just|another|perl|hacker/"
Thread Previous
|
Thread Next