Accessing class variables using a variable with the class name in perl

Question

I'm wondering how I would go about doing this:

package Something;
our $secret = "blah";

sub get_secret {
    my ($class) = @_;
    return; # I want to return the secret variable here
}

Now when I go

print Something->get_secret();

I want it to print blah. Now before you tell me to just use $secret, I want to make sure that if a derived class uses Something as base, and I call get_secret I should get that class' secret.

How do you reference the package variable using $class? I know I can use eval but is there more elegant solution?

Sinan Ünür · Accepted Answer · 2011-05-04 14:40:00Z

5

Is $secret supposed to be modifiable within the package? If not, you can get rid of the variable and instead just have a class method return the value. Classes that want to have a different secret would then override the method, instead of changing the value of the secret. E.g.:

package Something;

use warnings; use strict;

use constant get_secret => 'blah';

package SomethingElse;

use warnings; use strict;

use base 'Something';

use constant get_secret => 'meh';

package SomethingOther;

use warnings; use strict;

use base 'Something';

package main;

use warnings; use strict;

print SomethingElse->get_secret, "\n";
print SomethingOther->get_secret, "\n";

Otherwise, perltooc contains useful techniques to fit a variety of scenarios. perltooc points to Class::Data::Inheritable which looks like it would fit your needs.

answered May 4, 2011 at 14:40

Sinan Ünür

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Comments

Eugene Yarmash · Accepted Answer · 2011-05-04 08:35:15Z

3

You can use a symbolic reference:

no strict 'refs';
return ${"${class}::secret"};

edited May 4, 2011 at 8:35

answered May 4, 2011 at 8:30

Eugene Yarmash

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5 Comments

Gaurav Dadhania Over a year ago

Thanks Eugene, unfortunately our code has to use strict. Is there another way to reference it?

cjm Over a year ago

@Gaurav, why can't you turn off strict for that one line?

Gaurav Dadhania Over a year ago

@cjm Yes, I can turn it off for a line, but then it's just as un-elegant as using eval, and takes up 2 more LoC. :)

Dallaylaen Over a year ago

@Gaurav-Dadhania: no strict 'refs' is clearer. Once you've seen this construct, you'll never mistake it for anything else. eval only means that you have to parse more Perl by hand.

Eric Strom Over a year ago

turning off strict 'refs' is MUCH safer than a string eval. strict is a tool that you use to avoid errors, there is nothing wrong with turning it of for a few lines if you know you have to. strict is there to help, not to get in your way or limit the power of the language

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