91.pl

use v5.14;

package Student;
use Moose;
use Moose::Util::TypeConstraints;

subtype 'GradesArray', as 'ArrayRef[Int]';

coerce 'GradesArray', from 'Int', via { [ $_ ] };

has 'grades', is => 'ro', isa => 'GradesArray', coerce => 1;


package main;
my $s = Student->new( grades => 77 );

print $s->dump;