Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Depends on what you want it to do. You need to be aware that:
  • It won't work if it's in a module that you're importing elsewhere (because you end up changing Module::foo, which is irrelevant to the ModuleUser::foo that was imported).

    You can change that with

    no strict 'refs'; my $pkg = caller; *{ $pkg . "::foo" } = sub { ... }; # the final foo
    but only if that's what you want ("call once per user" instead of "call once globally").
  • There's no easy way to reset the trigger after it's fired. For your application, this is probably what you want, but you could imagine scenarios where it is not (eg mod_perl).
ikegami's lexical variable version gives "call once globally" semantics, without allowing resets (which you can trivially add by introducing another subroutine that captures the same lexical.) Same for the global variable, except resetting can be done directly.

Personally, I like the idiom

sub foo { our $CALL_COUNT; call_me_only_once() unless $CALL_COUNT++; stuff... }
But I'll admit I always wonder whether the code is going to get run 4.3 billion times and redo the init code...

In reply to Re: Is modifying the symbol table to redefine subroutines evil? by sfink
in thread Is modifying the symbol table to redefine subroutines evil? by tlm

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 all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others examining the Monastery: (8)
    As of 2018-06-22 22:02 GMT
    Find Nodes?
      Voting Booth?
      Should cpanminus be part of the standard Perl release?

      Results (124 votes). Check out past polls.