Challenge 3: A Role — Possible Solution
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package Describable;
use Moo::Role;

sub summary {
    my $self = shift;
    return "This is a " . ref($self);
}

package Widget;
use Moo;
with 'Describable';

package main;
use strict;
use warnings;
use feature 'say';

my $widget = Widget->new();
say $widget->summary();

Output:
This is a Widget

WHY THIS WORKS AS AN ANSWER
------------------------------
package Describable; use Moo::Role; reuses the chapter's own role-
declaration syntax exactly — Moo::Role (not plain Moo) is what marks
this package as a role rather than an ordinary class, per the
chapter's own note that a role "has no 'new', meant to be composed
in" rather than instantiated directly.

sub summary reuses the standard shift-self-first method pattern from
Chapter 3, still fully applicable here since a role's methods work
exactly like a class's own methods once composed in. ref($self)
returns the actual class name of whatever object summary() is called
on — here "Widget" — which is what lets this same role produce a
correct answer regardless of which class eventually composes it in,
rather than hardcoding "Widget" directly into the role itself.

package Widget; use Moo; with 'Describable'; reuses the chapter's own
composition syntax exactly — with 'Describable'; pulls summary()
directly into Widget, genuinely different from extends (Chapter 4's
own inheritance mechanism) since Widget never declares an @ISA-style
parent relationship to Describable at all, matching the chapter's own
description of roles as composed in, not inherited from.

$widget->summary() then calls the composed-in method exactly as if it
had been written directly inside Widget itself, correctly printing
"This is a Widget".