Re^2: need help with Tie::Judy

[expo1967]

Yes I have looked at the documentation for Tie::Judy and the example code is not complete. I need a complete functioning example.

[LanX]

> I need a complete functioning example.

try this

use Tie::Judy;

tie %fruit_color, 'Tie::Judy';

A hash represents a set of key/value pairs:

my %fruit_color = ("apple", "red", "banana", "yellow");

You can use whitespace and the '=>' operator to lay them out more nicely:

my %fruit_color = (
    apple  => "red",
    banana => "yellow",
);

To get at hash elements:

$fruit_color{"apple"};           # gives "red"

You can get at lists of keys and values with keys() and values().

my @fruits = keys %fruit_color;
my @colors = values %fruit_color;

see also Re: need help with Tie::Judy

[Bod]

I'm trying to understand what is happen with the sample code LanX has provided...

The command tie %fruit_color, 'Tie::Judy'; ties the associative array* %fruit_color to the class. From this point on, when %fruit_color is used, instead of the default Perl behaviour, the implementation is handled by Tie::Judy which implements alternative methods to the default methods used by Perl. In this case it does the same thing in a different way.

Is that something like correct?

* I deliberately didn't refer to %fruit_color here as a hash because in this case it is a Judy Array which is not a hash but another example of the same type of storage.

[LanX]

> Is that something like correct?

more or less, yes.

The tie() function binds a variable to a class (package) that will provide the implementation for access methods for that variable. Once this magic has been performed, accessing a tied variable automatically triggers method calls in the proper class. The complexity of the class is hidden behind magic methods calls.

see also perltie#Tying-Hashes

> I deliberately didn't refer to %fruit_color here as a hash

No it's for sure a "tied hash" in this case implementing a "hash". Both is correct.

Perl's generic term for associative arrays is "hash", no matter which implementation is used, so this is still a hash.

But a "tied hash" actually only refers to the %syntax and connected hash operators.

A tied hash may be used for any kind of magic, like e.g.

• making hash keys case insensitive $hash{key} eq $hash{KEY}
• returning the current time at different places $time{London}
• etc... see also Tie::Hash

But - besides providing a different implementations for hashes - it's in my experience mostly only used for syntactic sugar.

Most authors prefer providing an explicit OOP solution (like $time->get("London") ) and avoid the magic.