Re: Tieing and Blessing

[anazawa]

I posted similar question before. See also "Blessing tied hash".

By the way, tie() is one of my favorite functions. Tie::ToObject interests me specially.

[anaconda_wly]

I have the question is that firstly I didn't use DBM file yet and can't understand tie from its manual since lack the experience of dbm file. I think blessing is tieing a reference to a package actually.

[anazawa]

Though I don't understand how tie() works, too, I know how to use it ;) The following class represents a hash whose keys are case-insensitive:

package Insensitive::Hash;
use strict;
use warnings;

sub new {
    my ( $class, @args ) = @_;

    my %self;
    while ( my ($key, $value) = splice @args, 0, 2 ) {
        $self{ lc $key } = $value;
    }

    bless \%self, $class;
}

sub get {
    my ( $self, $key ) = @_;
    $self->{ lc $key };
}

sub set {
    my ( $self, $key, $value ) = @_;
    $self->{ lc $key } = $value;
}

1;

How can we use Insensitive::Hash?

use strict;
use warnings;
use Insensitive::Hash;

my $hash = Insensitive::Hash->new(
    'Content-Type' => 'text/plain',
);

# $key is case-insensitive
$hash->get( 'Content-Type' ); # => "text/plain"
$hash->get( 'content-type' ); # => "text/plain"

$hash->set( 'CONTENT-TYPE' => 'text/html' );

To implement tie() interface, rename the method names of Insensitive::Hash as follows:

package Insensitive::Hash;
use strict;
use warnings;

# new -> TIEHASH
# get -> FETCH
# set -> STORE

sub TIEHASH {
    my ( $class, @args ) = @_;

    my %self;
    while ( my ($key, $value) = splice @args, 0, 2 ) {
        $self{ lc $key } = $value;
    }

    bless \%self, $class;
}

sub FETCH {
    my ( $self, $key ) = @_;
    $self->{ lc $key };
}

sub STORE {
    my ( $self, $key, $value ) = @_;
    $self->{ lc $key } = $value;
}

1;

How tie() works?

use strict;
use warnings;
use Insensitive::Hash;

tie my %hash, 'Insensitive::Hash', ( 'Content-Type' => 'text/plain' );
# <=> my $hash = Insensitive::Hash->TIEHASH( ... )

$hash{'Content-Type'}; # <=> $hash->FETCH( 'Content-Type' );
$hash{'content-type'}; # <=> $hash->FETCH( 'content-type' );

$hash{'CONTENT-TYPE'} = 'text/html';
# <=> $hash->STORE( 'CONTENT-TYPE' => 'text/html' );

Insensitive::Hash was taken from "Object-oriented Perl" written by D. Conway. See also HTTP::Headers (field names are case-insensitive).