Not when the require() happens inside a conditional in the library consumer, which is what I was getting at. There's no point (and in fact it can't work) to call require() or use() for packages provided inline, so I presume both of us aren't talking about that case.

Consider the following structure shown below. The entire Foo:: package (and in fact the module file itself) is only loaded if the conditional is hit. This can be demonstrated by running an strace(1) (or your system's equivalent) against a call to that program both without, and then with the "load" parameter. This parameter in fact causes the module to be conditionally loaded, including the BEGIN code defined in the module.

File: consumer.pl

use strict;
use warnings;
use lib 'lib';

my $arg = shift // ''; 

if ($arg eq "load") {
  print "Now loading optional library.\n";
  require Foo;
  my $o = Foo->new;
  # Do stuff with $o here..
}
else {
  print "I skipped loading the optional library.\n";
  print "Try passing the 'load' option to load it.\n";
}
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File: lib/Foo.pm

package Foo;
use strict;
use warnings;

BEGIN {
  printf "BEGIN called from package %s\n", __PACKAGE__;
}

print "Class level logic.\n";

sub new {
  my $class = shift;
  $class = ref($class) || $class; # subclass boilerplate.
  print "constructor invoked for $class\n";
  return bless {}, $class;
}

1;
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