Re^4: Defining a sub within a sub: OK?


go ahead... be a heretic
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Re^4: Defining a sub within a sub: OK?

by ikegami (Patriarch)

on Oct 15, 2009 at 12:49 UTC ( [id://801345]=note: print w/replies, xml )

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in reply to Re^3: Defining a sub within a sub: OK?
in thread Defining a sub within a sub: OK?

It leaks memory.

use Devel::Peek;

sub foo {
    my $_recur;
    $_recur = sub {
        $_recur->();
    };

    my $x;

    Dump($x);
    Dump($_recur,0);
}

foo();
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SV = NULL(0x0) at 0x182a4d4
  REFCNT = 1
  FLAGS = (PADMY)
SV = RV(0x182a1e0) at 0x182a1d4
  REFCNT = 2
  FLAGS = (PADMY,ROK)
  RV = 0x2381a4
[download]

Compare the refcount of $x (which will get freed) to $_recur's (which won't).

The problem is that the sub referenced by $_recur captures $_recur, and thus you have a memory loop. If you wanted a lexical, you would need to use

sub foo {
    my $shared_with_all_recur = ...;

    my $_recur;
    $_recur = sub {
        ...
        $_recur->(...);
        ...
    };

    $_recur->(...);

    undef $_recur;
}
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This is a lot messier.