Using OO hash

[monk2b]

Hi Monks

I am creating a script using what I think are object oriented coding techniques. I am not able to get hash variables working properly. Could one of you let me know what I am missing here that would make my second print statement work properly.

my %BldEnv = (
  "TTT2" => {
    VersionOne => "one",
    VersionTwo => "two",
    VersionThree => "three",
    VersionFour => "four",
    }
);

# commented line works
#print "$BldEnv{TTT2}{VersionOne}\n";

# uncommented line doesn't work 
print "$BldEnv->{TTT2}->{VersionTwo}\n";

[moritz]

There is no OO involved in your example.

%BldEnv is a plain hash, and the values can be accessed with the $hash{$key} syntax.

The arrow -> is for references to hashes, blessed or not.

[monk2b]

Okay, I will use the first version. Thanks for the quick response.

[meraxes]

As moritz said, this isn't OO, but the second line will work with one small modification:

print "$BldEnv{TTT2}->{VersionTwo}\n";

Your version didn't work because the first -> was trying to dereference $BldEnv as though it were a reference to a hash. But WAIT! $BldEnv doesn't exist! You declared %BldEnv. Different animal! Despite using the $ sigil to get at hash values, when you added the -> after it, Perl was looking for a SCALAR variable and ignoring the HASH that you defined!

Perl's syntactic sugar allows you to get around derefencing the 'TTT2' hash using ->. As such, the first one is better.

Further to this, you really don't need to do string interpolation... can get a little messy with multi-level data structures. You could just do:

print $BldEnv{TTT2}{VersionTwo},"\n";

That way the variable is easier to see and prevents a number of interpolation pitfalls. If you're feeling adventurous, you could install the Perl6::Say module so you don't have to append that "\n" to the end like so:

use Perl6::Say;
say $BldEnv{TTT2}{VersionTwo};

The "\n" is auto-appended by say.

What you should _definately_ always do do is begin each script with:

use strict;
use warnings;

This would have thrown an error on your last print statement telling you that you that $BldEnv hadn't been declared, cluing you in that you're doing something wrong.

Happy Perl-ing!

update: expanded on difference between $BldEnv{key} and $BldEnv->{key}.

update the second: fixed errorneous variable naming.