philippe44 has asked for the wisdom of the Perl Monks concerning the following question:

Hi - I'm green to Perl and I'm having problem understanding some inheritance behavior. Maybe it's obvious but I'm missing it (I used to be C++)
The class structure is the following: I have 2 classes built on top of each other, on top of Socket IO::Socket::INET ==> remote ==> top
'remote' defines 2 methods : 'open' and 'request'
'top' overloads 'open' and add methods 'new' that is called by the application actually using it and a method 'sysread' to overload default read 
#pseudo code in class 'top'
sub new {
 my $class = shift;
 .
 .
 return open($class , $some_args);
}

sub open {
 my $class = shift;
 .
 .
 # I guess this is where the blessing of to $class happens ?
 my $sock = $class::SUPER->new($some_args);
 .
 .
 return $sock->request($some_args);
}

sub sysread {
 my $class = shift;
 .
 .
 $class::SUPER->read($var, 20);
 .
 .
 return $sock->request($some_args);
}

#pseudo code in class 'remote'
sub sysreadline(*;$) { 
    my ($handle, $maxnap) = @_;

        .
    $handle = qualify_to_ref($handle, caller());
        sysread($handle, $var, 10);
        .
}


sub request {
 my $self = shift;
 .
 sysreadline($self, 10);
 .  
}

[download]
What happens is that a call to "top::new", calls "top::open" that calls "remote::request" as expected and then in 'sysreadline', the call to 'sysread' calls IO::Socket::INET::sysread, not 'top::sysread'. I thought in IO::Socket::INET::new, the object was blessed as a 'top' so 'sysread' would call the overloaded one
After that, all subsequent call to 'sysread' by the application with a 'top' object call the overloaded 'sysread'
(NB: my "real" problem is about a multiple inheritance, but I'm trying first to understand a basic behavior here, sorry)

Replies are listed 'Best First'.
Re: inheritance problem
by hippo (Archbishop) on Oct 06, 2015 at 20:03 UTC

    Within your sub sysreadline the call to sysread is just a a plain subroutine call and not a method call. What happens if you make it a method call instead?

[reply]
[d/l]
[select]
      understood but so if the plain sysread is called, then what confused me a lot is that another app required a derivative of this code where SSL must be used to 'top' is inheriting from both 'remote' and 'IO::Socket::SSL' (I had to do that because I cannot modify the 'remote' class, I can only touch the descendant 'top') class
      base qw (IO::Socket::SSL remote);

      [download]
      With that, method calls will always try to be resolved in IO::Socket::SSL first, before going to IO::Socket::INET - this might be ugly and there might be a clean way to do that, I just don't know
      But although this works, now what happens is that the plain sysread (made in sysreadline) uses the overloaded sysread method in 'top'???
[reply]
[d/l]
        bummer ... got it now, it was a side-effect of adding a SSL socket. The calls to top::sysread were not made by 'request' but were made by the SSL negotiation !
[reply]
Re: inheritance problem
by GotToBTru (Prior) on Oct 06, 2015 at 19:56 UTC

    Try to create the shortest possible example that compiles and demonstrates the issue.

    Dum Spiro Spero
[reply]
Re: inheritance problem
by Anonymous Monk on Oct 07, 2015 at 01:15 UTC
    You're trying to use inheritance, that is your problem :)
[reply]

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