package Exp;

use 5.006;
use strict;
use warnings;
use Carp;

sub new{
	my $class = shift;
	my $validated = _validate( $_[0] );
	return bless {
		validated => $validated,
		stored	  => [],
	},$class;
}
sub _validate{
	croak "No arg!" unless $_[0];
	return $_[0];
}
sub store {
	my $self = shift;
	my $it = _validate( $_[0] );
	push @{ $self->{ stored } }, new( $it );  # <---here NOT OK	
}
1;

##</code><code>##

# croaks without arguments

perl -I . -MData::Dump -MExp -e " $exp=Exp->new(); dd $exp "

No arg! at -e line 1.

# OK with args

perl -I . -MData::Dump -MExp -e " $exp=Exp->new(2); dd $exp "

bless({ stored => [], validated => 2 }, "Exp")


##</code><code>##


perl -I . -MData::Dump -MExp -e " $exp=Exp->new(2); $exp->store(3) "

No arg! at -e line 1.


##</code><code>##

package ExpOk;

use 5.006;
use strict;
use warnings;
use Carp;

sub new{
	my $class = shift;
	my $validated = _validate( $_[0] );
	return bless {
		validated => $validated,
		stored	  => [],
	},$class;
}
sub _validate{
	croak "No arg!" unless $_[0];
	return $_[0];
}
sub store {
	my $self = shift;
	my $it = _validate( $_[0] );
	push @{ $self->{ stored } }, bless{ validated => $it },__PACKAGE__;  # <---here OK
}
1;


##</code><code>##

perl -I . -MData::Dump -MExpOk -e " $exp=ExpOk->new(2); $exp->store(3); dd $exp "

bless({ stored => [bless({ validated => 3 }, "ExpOk")], validated => 2 }, "ExpOk")