Using Pre-processor directive in Perl

cr_ashok has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Using Pre-processor directive in Perl by Corion (Patriarch) on May 13, 2005 at 07:05 UTC
Yes, it is possible. But no, you should not use it. There are two common ways of making code not run. One is to comment out code blocks with POD sections, but that cannot be done dynamically, and the other is to declare a subroutine as the toggle: `sub DEBUG() { 0 }; ... if (DEBUG) { print "We are here <--"; };` [download] There is (almost) no overhead with this method because Perl optimizes constant subroutines away.	[reply] [d/l]
Re: Using Pre-processor directive in Perl by salva (Canon) on May 13, 2005 at 07:11 UTC
you can use source filters for that, see perlfilter manual page... though most of the time it is a bad idea to do so. As Corion has already suggested, a better alternative is to use "if (Constant) {...}" constructions.	[reply]
Re: Using Pre-processor directive in Perl by spurperl (Priest) on May 13, 2005 at 10:26 UTC
I just want to add that there's a fundamental difference between C and Perl that makes "code disabling" preprocessor directives in Perl unnecessary. C is a compiled language, and preprocessor is for the compiler. What's #ifdef-ed out won't show up in the compiled code at all. This can boost performance and reduce the executable file size especially for multiplatform apps. Perl is not compiled, at least not in the sense C is, so it doesn't need such complications. A simple if (0) is good enough to exclude code from running. No preprocessor directive will make your code smaller to carry aroung.	[reply]
Re: Using Pre-processor directive in Perl by blazar (Canon) on May 13, 2005 at 08:45 UTC
`my %answer = ( possible => '-P', # See 'perldoc perlrun' recommended => 0 ); # Ditto as above!` [download]	[reply] [d/l]
Re: Using Pre-processor directive in Perl by Zaxo (Archbishop) on May 14, 2005 at 06:25 UTC
There is perl's -P flag; see perlrun. Better to learn the perly way of doing things. After Compline, Zaxo	[reply]