snippet.pl

#!/usr/bin/env perl
use 5.10.0;
use warnings;

{

    package Foo;
    use Moose;
    local $SIG{__WARN__} = sub { };
    has private => ( isa => 'Int' );
    has bar => (
        isa     => 'Int',
        is      => 'rw',
        trigger => \&update,
    );
    sub update { say 'the value of bar is ', shift->bar }
    no Moose;
    1;
}

my $foo = Foo->new();
$foo->bar($_) for 1 .. 5;

warn 'warns but does not die';

exit 0;

how to switch off warnings in a moose class (if you must), see here for motivation