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Re: [Omaha.pm] Class::Date - change once set

Forwarding dLux's message.

j


From: "Balázs Szabó (dLux)" <dlux@dlux.hu>
Date: November 11, 2005 3:06:01 AM CST
To: Jay Hannah <jay@jays.net>
Subject: Re: [Omaha.pm] FW: FW: Class::Date - change once set

Hi,

Jay Hannah wrote:


From: "Balázs Szabó (dLux)" [mailto:dlux@dlux.hu]


use Class::Date qw(date);
$a = date "2000-11-11";
$b = date "1970-10-21";

print "a: $a, b: $b\n";
swap1($a, $b);
print "a: $a, b: $b\n";

sub swap1 {
   $x = $_[0];
   $_[0] = $_[1];
   $_[1] = $x;
}



Ahhh, yes. I misread your email the first time. To make sure I know
what's happening let me walk through it...


Ok.




sub swap1 {



$a is obj in year 2000. $b is obj in year 1970. $_[0] is a ref to $a.
$_[1] is a ref to $b.


Correct.


   $x = $_[0];
$x is created, a new obj in year 2000. (via clone() inside Class::Date) 

Not correct.  $_[0] is always points to the same object as $a, $_[1]
always points to the same object as $b; In this case, we have a new
object, $x, which is also points to the same as $a and $_[0];


   $_[0] = $_[1];


$a obj is destroyed. A new $a is created, year 1970.  (via clone()
inside Class::Date)


Not correct. Now $a is points to the original $b, while $x keeps the
reference to $a;


   $_[1] = $x;
}


$b obj is destroyed. A new $b is created, year 2000.  (via clone()
inside Class::Date)

Is that right?


Not correct. $b now points to the $x, which kept the reference to the
original $a, and in the previous step, we saw that $a is now pointing to
the original $b;



Thanks,

j


So, it does not copy OBJECTS, it just increasing and decreasing
reference counters to objects (since perl is a reference-counting language). 

Please see the perlobj and perlref (or perlreftut) manual to get what I
had talked about.

Regards,

--

Szabó Balázs (dLux)
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