http://www.perlmonks.org?node_id=542085


in reply to Re: recursive anonymous subroutines
in thread recursive anonymous subroutines

"What's wrong storing a reference to an anonymous inner sub in an anonymous outer closure?"
It's a recursive, i.e. leaking, reference.

Replies are listed 'Best First'.
Re^3: recursive anonymous subroutines
by snoopy (Curate) on Apr 10, 2006 at 04:28 UTC
    It's a recursive, i.e. leaking, reference.

    Hmm... probably safer to keep the reference on the call stack, thus releasing it on exit.

    For example, adopting the convention that the reference is always passed as the first parameter: 

    my @factorials = map {

    $_[0] ||= sub {
        my $factor = pop;

        return $factor > 1
            ? &{$_[0]}($_[0],$factor-1) * $factor
            : 1;
    };

    &{$_[0]}($_[0],$_)} (3,5,7,9);

    [download]
    ..or.. 
    sub make_call {
    goto $_[0];
}

my @factorials = map {

    make_call (sub {
        my $factor = $_[1];
    
        return $factor > 1
            ? make_call($_[0], $factor-1) * $factor
            : 1;
    }, $_);

} (3,5,7,9);

    [download]
[reply]
[d/l]
[select]
      Very nice! I believe your make_call version will shortly become a new idiom in my code. Many thanks!
[reply]
[d/l]
      Just thought I'd point out that this is an interesting reinvention of a previous post (though with one less level into the call stack due to the goto). Compare:
      # Your's:
sub make_call { goto $_[0] }

# Anonymonk's(slightly rearranged):
sub Y { $_[0]->(@_) }

      [download]
      Update: Well, it's more the same if you change your call to:
      make_call (sub {
        my $factor = $_[1];
   
        return $factor > 1
            ? $_[0]->($_[0], $factor-1) * $factor
            : 1;
    }, $_);

      [download]
[reply]
[d/l]
[select]
[reply]
[d/l]

In Section Seekers of Perl Wisdom