arrays of object in OO perl

IL_MARO has asked for the wisdom of the Perl Monks concerning the following question:

Hi guys,
here is my problem:
You have a class, say, called Animal. Animal has a feature called DNA, and DNA is an array. Example:

package Animal;
# constructor
sub new {
    my $this = {};
    # object properties
    $this->{DNA} = [];

    bless $this;
    return $this;
    }

sub getDNA
    {
    my $this = shift;
    return "@{$this->{DNA}}";
    }

sub setDNA
    {
    my $this = shift;
    @{$this->{DNA}} = @_;
    return @{$this->{DNA}};
    }
[download]

Now, imagine you want to create another class, say, called Population. And you want a bag of Animals, like:

package Population;
use Animal;

# constructor
sub new {
    my $this = {};
    # object properties
    $this->{individual} = [];

    bless $this;
    return $this;
    }

sub init {
        for ($i=0; $i<5; $i++) { 
         my $empl = Animal->new();
             $empl->setDNA(4, 6, 8, 10);
         push (@{$this->{individual}}, $empl);
    }
}
[download]

As you can see, the method init simply pushes 5 not empty Animals into a Population object.
The problem is that I'm not able to access them! What I should do if I want, say, set the DNA of a specific Animal of the Population?
And what if want to get or set a specific value of a specific slot of the DNA of an Animal...? I lack the knowledge I need. I tryied in many ways. Just an example, if I want to get the DNA of the Animal in the first slot:

sub getTheFirst{
    my $this = shift;
    return @{$this->{individual}}[0]->getDNA();
}
[download]

But of course it's not working.
I can't get what I want...

Comment on arrays of object in OO perl Select or Download Code

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Re: arrays of object in OO perl by ikegami (Patriarch) on Nov 19, 2008 at 06:17 UTC
Use `use strict;`! There's a major error in `init`. As for the problem with `getTheFirst`, since it would be `$array[0]->getDNA()` if you were dealing with an array instead of a reference to an array, then it's `${$array_ref}[0]->getDNA()` when using an array ref. It can also be written as `$array_ref->[0]->getDNA()` So all together, we get $this->{individual}->[0]->getDNA()</c> See Dereferencing Syntax References Quick Reference perlref perlreftut	[reply] [d/l] [select]
Re^2: arrays of object in OO perl by IL_MARO (Initiate) on Nov 19, 2008 at 06:47 UTC
Guys, may the allmighty Spaghetti Monster bless you all! I used strict, as suggested; I corrected all the mistakes. And now it works. I know, THOU SHALL USE STRICT... but I was lazy. Now I made another step toward enlightment. Thanks again. EDIT: it's not working... I mean: if I use the first slot of the array, it works: `return $this->{individual}->[0]->getDNA();` But if I use another slot, it turns out that is undefined. `return $this->{individual}->[2]->getDNA();` This means that I don't have an array of 'individual', despite I pushed 5 of them into the array. Mmm... `sub init { my $i; foreach $i (0 .. 4) { my $this = shift; my $empl = Animal->new(); $empl->setDNA(4, 6, 8, 10); push (@{$this->{individual}}, $empl); print " ".$i."\n"; print $this->{individual}->[$i]->getDNA(); } }` [download] In this way, the output is `0 4 6 8 10 1 Can't call method getDNA ...` [download] And thus definitively I don't have and array of `Animal`, but `individual` is just a scalar. Damn.	[reply] [d/l] [select]
Re^3: arrays of object in OO perl by ChOas (Curate) on Nov 19, 2008 at 07:50 UTC
You want to take the `my $this = shift;` [download] Outside of the for-loop. GreetZ!, ChOas print "profeth still\n" if /bird\|devil/;	[reply] [d/l]
Re^4: arrays of object in OO perl by IL_MARO (Initiate) on Nov 19, 2008 at 07:57 UTC
Re: arrays of object in OO perl by gwadej (Chaplain) on Nov 19, 2008 at 04:58 UTC
Unfortunately, the biggest problem with using references seems to be getting the syntax right. Try thi: `sub getIndividual{ my $this = shift; my $index = shift; return $this->{individual}->[$index]->getDNA(); }` [download] The problem with your version was you were trying to call a method on an array slice. G. Wade	[reply] [d/l]
Re^2: arrays of object in OO perl by IL_MARO (Initiate) on Nov 19, 2008 at 06:34 UTC
I tried with the suggested code `return $this->{individual}->[$index]->getDNA();` but the output is always the same: `Can't call method "getDNA" on an indefined value at Population.pm ...` I want to point out that I don't push into Population empty arrays.	[reply] [d/l] [select]
Re: arrays of object in OO perl by ikegami (Patriarch) on Nov 19, 2008 at 06:14 UTC
Use `use strict;`! There's a major error in `init`.	[reply] [d/l] [select]
Re: arrays of object in OO perl by matrixmadhan (Beadle) on Nov 19, 2008 at 06:10 UTC
Would you mind if I say a small change? This is c-style looping `for ($i=0; $i<5; $i++) {` should be as `foreach my $i ( 0 .. 4 ) {`	[reply] [d/l] [select]
Re^2: arrays of object in OO perl by GrandFather (Saint) on Nov 19, 2008 at 08:49 UTC
The counter isn't used so the range is better expressed 1 .. 5. Perl reduces RSI - it saves typing	[reply]
Re^3: arrays of object in OO perl by matrixmadhan (Beadle) on Nov 20, 2008 at 04:20 UTC
Actually it is used, to indicate/display the running number. So, the counter is needed `push (@{$this->{individual}}, $empl); print " ".$i."\n"; print $this->{individual}->[$i]->getDNA();` [download]	[reply] [d/l]
Re^4: arrays of object in OO perl by GrandFather (Saint) on Nov 20, 2008 at 04:34 UTC