How to hide method from base class in a way `can` do not see it?

user_4632019 0
Viewed 66

I try to hide method from base class by just forward declare subroutine like:

sub xid;

If I call this method I get expected error:

DBG> $tuple->xid
ERROR: Undefined subroutine &HyperMouse::Schema::Result::SaldoAnal::xid called at (eval 2346)[/home/kes/perl5/perlbrew/perls/perl-5.24.1/lib/site_perl/5.24.1/DB/Hooks.pm:422] line 8, <STDIN> line 13.

but $tuple->can( 'xid' ) still return true value:

&HyperMouse::Schema::Result::SaldoAnal::xid

How can I hide xid method, so $tuple->can( 'xid' ) return false instead of:

&HyperMouse::Schema::Result::SaldoAnal::xid
perl inheritance oop
2 Answers

You can override can.

Hide all existing-but-undefined subs:

sub can {
   my $self = shift;
   my $cv = $self->SUPER::can(@_)
      or return undef;
   defined(&$cv)
      or return undef;
   return $cv;
}

Hide a specific sub:

sub can {
   my $self = shift;
   my $cv = $self->SUPER::can(@_)
      or return undef;
   $cv == \&xid
      and return undef;
   return $cv;
}

Your whole attempt to hide a method of the base class is a very strange thing to do. Causing the call to fail would be less surprising.

sub xid {
   croak("Not supported.");
}

But that doesn't really hide the stink of poor class design.

Whichever hack you use, it's entirely bypassable using

$tuple->Base::Class::xid()
user_5899240

can works because the method name is still present in your class's symbol table, but it points to undef. You have to write your own override for can.

sub can {
  my($self) = shift;
  my($method) = @_;

  return undef if $method == "xid";
  return $self->SUPER::can($method);
}

However, this means your subclass now violates its base class's interface, it does not behave like the base object. This indicates poor design. Consider a different approach, subclassing may be inappropriate. Try composition instead.

user_146600
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