A simple Comparison

[vtprogrammer]

How do you compare two objects. I used if ($Part eq $PN) { do stuff; } But the comparison doesn't work. I've tried using "==" but that doesn't work either. It never equals even when they are exactly the same. Any suggestions?

[btrott]

If you compare them using eq or ==, all you're doing is comparing their values as references. And since they're two different objects--ie. not references to the same object--they're two different references. So they won't be equal.

To do a proper object comparison, you'll need to write a method that compares two of your objects. One possibility would be to serialize the objects and compare the serialized strings:

    my $obj1 = new Obj;
    my $obj2 = new Obj;

    ## The two objects above are now equal, let's say.
    ## Serialize them, then compare the serialized
    ## data.

    use Storable qw/freeze/;
    if (freeze($obj1) eq freeze($obj2)) {
        ## They're the same.
    }

In fact, you could even use overload to overload the comparison operator so that the proper comparison happens automagically:

    package Obj;
    use Storable qw/freeze/;
    use overload '==' => \&compare;

    sub compare { return freeze($_[0]) eq freeze($_[1]) }

Now you can just say:

    if ($obj1 == $obj2) {
        # They're the same.
    }

[[e-mail]]

This doesn't work if one or both of the objects is global, Storable::freeze will fail with "Can't store GLOB items".

[choroba]

GLOB and "global" are two different things. You can easily freeze global variables, but you can't freeze typeglobs, see "Typeglobs and Filehandles" in perldata.

use Storable;
bless our $x = [], 'My::class';
print Storable::freeze($x);         # No error, $x is global.

bless my $y = \*STDERR, 'My::class';
print Storable::freeze($y);         # Can't store GLOB items, $y is le
+xical.