Foo.pm:

package Foo;

use strict;
use warnings;

sub new {
  return bless {};
}

sub method {
    return 1;
}

1;
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script.pl:

#!/usr/bin/perl
use strict;
use warnings;
require Foo;

my $class = 'Foo';
my $obj = bless {}, $class;

print $obj->method;
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Works fine, but if you remove the require Foo; line, you get the error Can't locate object method "method" via package "Foo" at script.pl line 9. perl needs the require statement to find and compile the source files.