Comment on

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->(@_);
}
[download]

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]->(@_);
}
[download]

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;
    ...
  }
}
[download]

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

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:
	&		`&`
	<		`<`
	>		`>`
	[		`[`
	]		`]`

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.


There's more than one way to do things
	PerlMonks