Named subs capture at compile-time, which is problematic for nested subs. Anon subs capture at run-time.

Furthermore, there's no advantage to nesting named subs. They can be called from anywhere just as if they weren't nested.

What follows demonstrates the above points.

Named: 

use strict;
use warnings;

sub outer {
   my ($x) = @_;

   sub inner { # XXX bad
      print("$x\n");
   }

   inner();
}

outer(4);
outer(5);
inner();

[download]
Variable "$x" will not stay shared at a.pl line 8.
4
4    # XXX Want 5.
4    # XXX Don't want inner sub to be public

[download]

Anon: 

use strict;
use warnings;

sub outer {
   my ($x) = @_;

   local *inner = sub {
      print("$x\n");
   };

   inner();
}

outer(4);
outer(5);
inner();

[download]
4
5
Undefined subroutine &main::inner called at a.pl line 16.

[download]

Note that inner isn't totally private in the last example. It can be done, but what I posted is a good compromise of privacy and code clarity.

Update: Initially forgot to mention the useless nesting of named subs. Added.

In reply to Re: named subs within named subs by ikegami
in thread named subs within named subs by perl5ever

Title:
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, details, 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, summary, 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.