the text gets into the object as shown by Data::Dumper.

Yes it does ... doesn't mean there is an accessor created (accessors are just "methods" aka "subroutines")

without has bar

use Data::Dump qw/ dd /;
dd( my $f = Foo->new(qw/ bar 1 /) );
$f->bar;
{package Foo; use Moo; }
__END__
bless({ bar => 1 }, "Foo")
Can't locate object method "bar" via package "Foo" at - line 3.
[download]

you can cheat and use $f->{bar} ... this is cheating / breaking encapsulation / peeking inside object / not using official api / so if sometime in the future you internally rename bar attribute to barps, anyone using ->{bar} would have to update program, anyone using the documented api ->bar wouldn't (because you'd update that too) ... yeah seems convoluted example but thats how they work :)

with has bar Without BEGIN block there is no bar accessor (accessor is subroutine ... all $obj->whatever is subroutines)

use Data::Dump qw/ dd /;
dd( my $f = Foo->new(qw/ bar 1 /) );
$f->bar;
{package Foo; use Moo; has( qw/ bar is rw / ); }
__END__
bless({ bar => 1 }, "Foo")
Can't locate object method "bar" via package "Foo" at - line 3.
[download]

with has bar and With BEGIN block no death :)

use Data::Dump qw/ dd /;
dd( my $f = Foo->new(qw/ bar 1 /) );
$f->bar;
BEGIN{package Foo; use Moo; has( qw/ bar is rw / ); }
__END__
bless({ bar => 1 }, "Foo")
[download]

with has bar and Without begin block no death (moved to line 1)

{package Foo; use Moo; has( qw/ bar is rw / ); }
use Data::Dump qw/ dd /;
dd( my $f = Foo->new(qw/ bar 1 /) );
$f->bar;
__END__
bless({ bar => 1 }, "Foo")
[download]

got that? See also perlobj, A Method is Simply a Subroutine, Attributes