{ __syntax } question

[capitano]

I'm learing about XML:arser and looking at an example snippet of code in the Wrox book "Professional Perl development".

There is a snippet of code which does a funny syntax thing with curly-brackets and I don't understand it:

sub Init {
my $self = shift;

$self->{__myData} = {
invoice_number => "",
customer_id => "",
address => "",
name => "",
#.... and more code
};
#...and more code
}

Specifically, this is the part I'm not understanding:

$self->{__myData}

??? What is {__myData} ??

Thanks for any help here.

Bryan

 

[justice41]

[tt]$self[/tt] is a reference to a hash (actually $self is a reference to an object in this case, but objects are usually stored as hashes; although they need not be). Just as you would access a hash as

$hash{'akey'} = 'myvalue';
print "Value of $key is $hash{$key}\n";

You can also define a reference to a hash like

my $hashref = \%hash;

And you would access the hash value as
[/code]
$hashref->{'akey'} = 'myvalue';
#or equivalently
$$hashref{'akey'} = 'myvalue';
print "Value of $key is $hashref->{$key}\n";
[/code]
Just as you can define hashes like

%hash = ( key1 => 'value1',
          key2 => 'value2',
        );

You can also define hash refs like
(note the braces instead of parentheses)

$hashref = { key1 => 'value1',
             key2 => 'value2',
           };

In your case $self is a reference to an object, a hash reference that has been blessed into a class. The class being whatever package the Init() sub is contained in.

It is common in packages and modules put an underscore before a hash key that is internal to the module. Meaning it isn't meant to be accessed outside the package, only through methods contained in the module. You can, of course access them in you code by using the key, it's just not part of the 'published' interface of the module.

See the perlref perldoc for more.

http://perldoc.com/perl5.8.0/pod/perlref.html

jaa