#!/usr/bin/perl --
use strict;
use warnings;
use Data::Dump;
use IO::File;

Main( @ARGV );
exit( 0 );

BEGIN
{
    package Shack;
    use Moo;
    has(
        qw/
            crabs
            is rw
            required 1
            init_arg base
        /,
        builder => sub {
            warn "## BUILDER { @_ } @{[Data::Dump::pp( @_ )]}\n";
            IO::File->new( $_[0] ) or die qq{"$_[0]": $!\n$^E\n };
        },
    );
    $INC{'Shack.pm'} = __FILE__;
}

sub Main {
    use Shack;
    dd( Shack->new( base => __FILE__ ) );
    dd( Shack->new( crabs => __FILE__ ) );
}

__END__
bless({ crabs => "crabshack.pl" }, "Shack")
## BUILDER { Shack=HASH(0xc3f7ec) } bless({}, "Shack")
"Shack=HASH(0xc3f7ec)": No such file or directory
The system cannot find the file specified
  at crabshack.pl line 23.