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

I consider it a bad idea to define a named sub within another sub

I agree 100%. Anon subs are another story. For example, I use constructs such as 

sub foo {
    my $shared_with_all_recur = ...;

    local *_recur = sub {
        ...
        _recur(...);
        ...
    };

    _recur(...);
}

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Re^3: Defining a sub within a sub: OK?
by AnomalousMonk (Archbishop) on Oct 15, 2009 at 08:08 UTC
    Aside from the fact that the approach given in your reply is 'cleaner' and therefore, to my mind, preferable to something like 
    sub foo {
    my $shared_with_all_recur = ...;

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

    $_recur->(...);
}

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    is there any advantage to using a localized glob rather than a lexical scalar?
[reply]
[d/l]

      It leaks memory. 

      use Devel::Peek;

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

    my $x;

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

foo();

      [download]
      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;
}

      [download]

      This is a lot messier.

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