#!/usr/bin/perl
use warnings; use strict;
use P;
use parent 'Switches';

## example of a PERL compile-time constant 
## based on a command line argument "-NODEBUG"
## using 'Switches' & BEGIN

## to run, place "-DNODEBUG" on the command line. (law)

BEGIN {
  Switches->process_options({DNODEBUG => 
      { act => [ sub { eval '# line '.__LINE__.' "'.__FILE__.'"
                            use constant "_NODEBUG_"=>1;';
                        $@ && P::Pe("eval: %s\n", $@);
          } ], } }, \@ARGV);
  eval 'use constant _NODEBUG_ => undef;' unless *main::_NODEBUG_{CODE};
}

sub declared ($) {
   use constant 1.01;              # note: needed for "declared", below
   my ($name, $pkg) = (shift, caller);

   # prepend module name (must be a full-name)
   $name = q(main) . $name if '::' eq substr $name,0,2;

   # use caller pkg if needed
   my $full_name = 0 <= index($name,'::') ? $name : $pkg.'::'.$name;
   $constant::declared{$full_name};
}


P "_NODEBUG_ is a %s %s", declared(q(_NODEBUG_)) ?  "constant" : "sub",
P "and is %s", _NODEBUG_ ? 
  "TRUE  (devel checks disabled)." :
  "FALSE (devel checks enabled)."