This is really easy to achive. perl will optimize away sections enclosed in if blocks with constant conditions:

$ perl -MO=Deparse -le '
> sub DEBUG () { 1 }
> if(DEBUG) { print "Debug" }
> print "Done";
> '
BEGIN { $/ = "\n"; $\ = "\n"; }
do {
    print 'Debug'
};
print 'Done';
-e syntax OK

$ perl -MO=Deparse -le '
> sub DEBUG () { 0 }
> if(DEBUG) { print "Debug" }
> print "Done";
> '
BEGIN { $/ = "\n"; $\ = "\n"; }
'???';
print 'Done';
-e syntax OK

[download]

So with a false constant, perl will replace the if with a statement B::Deparse doesn't like (but is probably a noop). With a true constant, it gets enclosed in a do block (in case there are any lexicals declared--perl doesn't look ahead far enough to know).

(And I say 'perl', not 'Perl', because it's possible that a different implementation of Perl, should there ever be one (Ponie?), may apply different optimizations.)

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

: () { :|:& };:

Note: All code is untested, unless otherwise stated

In reply to Re: Debug code out of production systems by hardburn
in thread Debug code out of production systems by liz

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.