See $! in perlvar. You can't reliably set $!. If you have warnings on, you'll get Argument "Error loading data!" isn't numeric in scalar assignment because $! isn't a normal variable, and expects a numerical system error code. (Re: warnings, see Use strict warnings and diagnostics or die).

The usual way of indicating a failure in Perl is to die, which functions as an exception that can be caught downstream, e.g.

sub new{
    my $class = shift;
    my $self;

    $self->{name} = 'new';
    bless ($self);

    if ($self->loaddata()){
        return $self;
    }else{
        die "Error loading data!";
    }
}
[download]

which could be invoked as my $obj = eval{coolobject->new} or die "$@";

If you absolutely want to pass an error and return an undef, you could set $@ manually, but this is probably poor form.

If you are rolling your own objects for fun/education, I'd recommend you look at perltoot. If you are rolling objects for deployment, I'd look at (and use) some prior art like Moose, Mouse...

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