|
Posted by Koszalek Opalek on November 28, 2007, 3:07 pm
Please log in for more thread options
Hello,
I overloaded the quotes '""' in my class by using
use overload ('""' => \&getDesc);
I was hoping it will allow me to write
print ("Hello from object $obj.\n");
instead of
print ("Hello from object " . $obj->getDesc() . ".\n");
Well, it works that way but there are side effects that break my class
completely.
Problem 1)
Before overloading, statement
if ($obj)
is true, if $obj is a reference to any object of class Obj.
If the reference is undef, $obj is false.
After overloading "", $obj is also false if getDesc() happens to
return an empty string! That's not what I wanted. If I did, I could
use
if ("$obj")
Problem 2)
Before overloading I could compare object references
if ($obj1 == $obj2)
and check if they point to the same location/object. I can no
longer do that once the '""' operator has been overloaded.
Operation "==": no method found,
left argument in overloaded package Obj,
right argument in overloaded package Obj at ./a.pl
line 38.
I can use eq instead of == if I also add falllback => 1 to the
overload pragma but that string-compares $obj1->dummy()
with $obj2->dummy() instead of object references. Again, if
I wanted to compare the string representation I could do
if ("$obj1" eq "$obj2")
Am I doing sth wrong or miss the point completely? Or is this
overload module broken?
I enclose a short listing that demonstrates my point.
Uncomment one of the #use clauses to see how it breaks(?)
things. Any help will be appreciated.
#!/usr/bin/perl
use strict;
use warnings;
{
package Obj;
#use overload ('""' => \&getDesc);
#use overload ('""' => \&getDesc, fallback => 1);
sub new ()
{
my $class = shift;
my $self = {};
bless $self, $class;
}
sub getDesc ()
{
return "";
};
};
my $obj1 = Obj->new();
my $obj2 = Obj->new();
### PROBLEM 1 ###
if ($obj1) {
print "true\n";
} else {
print "false\n";
};
### PROBLEM 2 ###
if ($obj1 == $obj2) {
print "same references\n";
} else {
print "different references\n";
};
__END__
I originally posted it to comp. lang perl. misc but maybe *.modules
is better suited for this.
Koszalek
| 
XML Sitemap