Beefy Boxes and Bandwidth Generously Provided by pair Networks
Your skill will accomplish
what the force of many cannot
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
  • Actually you can redefine subroutine by using eval "sub func {'...'}"

That would create a new function at runtime, but it wouldn't follow the rules of dynamic scoping (see MOPT-03 for details).

As you've used it, the eval() just binds a new function to the name 'func'. To be dynamic, the new version of func() would have to be restricted to the evaluation context of the function that defined it:

$VAR = "old VAR"; sub func {return ("old func()")} sub show {printf "VAR='%s', func()='%s'\n", $VAR, func()} sub redefine { eval 'sub func {return ("new func()")}'; local ($VAR) = "new VAR"; show(); } show(); redefine(); show();

returns:

VAR='old VAR', func()='old func()' VAR='new VAR', func()='new func()' VAR='old VAR', func()='new func()'

which shows the difference between redefining a globally-scoped function and re-binding a dynamically-scoped variable.

  • and better yet is just to use anonymous subroutines and use ordinary variables to switch between different ones:

Yes, that would work:

$VAR = "old VAR"; $FUNC = sub {return ("old func()")}; sub show {printf "VAR='%s', func()='%s'\n", $VAR, &$FUNC()} sub redefine { local ($FUNC) = sub {return ("new func()")}; local ($VAR) = "new VAR"; show(); } show(); redefine(); show();

returns:

VAR='old VAR', func()='old func()' VAR='new VAR', func()='new func()' VAR='old VAR', func()='old func()'

which does the right thing. But to get the effect of a dynamically-scoped function, you have to use a dynamically scoped (aka: local) variable, and I did say that in the original article.

HOWEVER.. check out the next reply to see how I was, in fact, wrong.


In reply to Re2: MOPT-04 - identification, part 2 by mstone
in thread MOPT-04 - identification, part 2 by mstone

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!
  • 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?
    Username:
    Password:

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

    How do I use this? | Other CB clients
    Other Users?
    Others scrutinizing the Monastery: (5)
    As of 2015-07-06 00:02 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (68 votes), past polls