When you write

has fif => ( is => 'rw' );
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Moose creates:

• one attribute called $self->{fif} (that you should not use anyway, encapsulation and all that)
• one reader accessor method called $self->fif
• one writer accessor method called $self->fif($value)

  (actually, the last two are just one method IIRC...)

When you write

has fif => ( is => 'rw', reader => '_fif' );
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,Moose creates:

• one attribute called $self->{fif} (that you should not use anyway, encapsulation and all that)
• one reader accessor method called $self->_fif
• one writer accessor method called $self->fif($value)

When you subsequently write

sub fif { ...... }
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you are creating another method, that has nothing to do with the others. But, as convention in perl is that _methods beginning with an underscore are private, people will call the $self->fif method to read the attribute so they won't see the value unless the password thing is true. Silly, not great security, but that is that.