Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
One problem with using dynamic scoping is that you've opened up the possibility that the same variable could be used somewhere else for a different purpose. That is the advantage to using lexicals.

Another solution is to use ReleaseAction to do cleanup when you exit the sub.

sub outer { my $helper; $helper = sub { ... }; my $delay_cleanup = on_release {$helper = undef}; $helper->(@_); }
Effectively it does the same thing as the weaken solution, but the code is a little more explicit about what is happening, when. I'd personally lean towards this solution.

And a final option. Larry thinks that using dynamic scoping on lexical variables is too confusing to allow. But he does allow it for data structures. Which leads to the convoluted:

sub outer { my @helper; local $helper[0] = sub { ... }; $helper[0]->(@_); }
I wouldn't suggest this solution for fear of the psychopathic maintenance programmer demanding to know why this works. But every year or two I wind up using this fact in a recursive function to detect and track down potential deep recursion bugs. For instance I'm recursing through a set of nodes and I'll do something like this:
{ my %in_node; sub something_recursive { my $node = shift; if ($in_node{$node->{name}}) { confess("Can't access $node->{name} while accessing $node->{name +}"); } local $in_node{$node->{name}} = 1; ... } }

In reply to Re: Creating Nested Functions by tilly
in thread Creating Nested Functions by ikegami

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others pondering the Monastery: (3)
    As of 2020-11-28 05:18 GMT
    Find Nodes?
      Voting Booth?

      No recent polls found