On 11/03/2006 04:57 AM, Rob Dixon wrote:
Mumia W. wrote:
>
On 11/03/2006 02:23 AM, Muttley Meen wrote:
In the attached script I implement two packages:
Package1 and Package2.
Package2 is derived from Package1, which I guess I dont well.
Now Package1 has a method called IncErr which increments a variable
named $err.
If I call something like:
$a = Package1::new();
$a->IncErr();
print "ERR1: $a->{err}\n"; # should print 1
all goes well, but if I call something like:
$a = Package1::new();
$a->Package2->Create(); # this should call IncErr too
This is not allowed because "Package2" is not a method within the
class Package1. You want this:
Yes it is! It's an accessor method (albeit written wrongly). This is
indeed a
very tangled web!
Yeah, I should've looked more closely at Muttley's program.
my $b = Package2->new();
$b->Create();
print "ERR(\$b): $b->{err}\n";
print "ERR1: $a->{err}\n"; # should print 1
doent't work as I expected.
Is there something wrong with the way I `bless`-ed the class Package2 ?
------>8-----------
#! /usr/bin/perl
use strict;
use warnings;
# Modify your program to work with these.
Amen.
package Package1 ;
sub new {
my ($class) = @_;
$class = __PACKAGE__ ;
print "Call new [".$class."]\n" ;
$r = [];
$this = {};
$class->{err} = 0 ;
$r->[0] = Package2::new($this->{sock_fd} );
bless $this, $class;
return $this ;
}
sub IncErr {
my $this = shift ;
$this->{err} += 1 ;
}
sub Package2 {
my $this = shift ;
@_ ? ($r->[0] = shift) : $r->[0];
}
package Package2 ;
@ISA = ("Package1");
sub new {
my ( $this, $sock ) = @_ ;
$class = __PACKAGE__ unless @_;
$this->{sock_fd} = $sock ;
bless $this;
return $this ;
}
sub Create {
my $this = shift;
print "Call Create\n" ;
print "ERR2: $this->{err} ( this should print 2 )\n" ;
$this->IncErr() ;
print "ERR2: $this->{err} ( this should print 3 )\n" ;
}
my $a = Package1::new();
$a->IncErr();
$a->IncErr();
$a->Package2->Create();
print "ERR1: $a->{err} ( this should print 3 )\n" ;
------------------->8--------------------
I didn't look in detail at your program, but I also see that you use a
suboptimal syntax for creating objects; don't use "::"; use "->", e.g.
my $a = Package1->new();
>
Using "::" will work, but it creates problems that will make you
sad--such as preventing inheritance.
Is worse than suboptimal - it's wrong! Package1::new() won't pass the
package
name as the first parameter. You could write the constructor differently of
course so that it fixes the call, but that's not how it's supposed to work.
Using "use strict" and "use warnings" will help you catch errors like
the one above where you do "$a->Package2->Create()"
Not true, but still an essential technique.
Rob
And I should've tested that. :-(
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