Can I know which child class am I from parent's code in Moose?

Question

I am creating a set of small Perl programs which will be run like a CLI. I want all of them to share some features, eg. same input/output format (probably JSON). I also want each component to be black-box testable with mock arguments. This is what I have so far:

• A number of modules actionA.pm, actionB.pm... actionZZZ.pm, one for each component/operation. All of them will use Moose and should have a sub run {...} which will receive a data hasref/object with the operation's input parameters, and any handle (database, filesystem, whatever) they need to use, and return a data hashref/object with the operation's output parameters.

• A Moose role which requires 'run' and is consumed by every actionX.pm module, forcing them to implement run.

• Additional Moose roles and/or superclasses for certain subsets of the actionX.pm modules, so they can consume them to specify wether they need their run method to be provided with a database handler, a filesystem handler, etc.

• A common Moose superclass (don't know if this really needs to be either Moose nor a superclass, just want this to be a fairly simple one-liner on each actionX.pm), let's call it abstractAction.pm, for all of the actionX.pm classes, which converts them into some sort of Modulino (see below).

What I want to achieve with this is that, when I run perl actionX.pm arguments from command line, some code in abstractAction.pm will:

1. Read JSON/whatever from @ARGV and convert it to Perl data structures.

2. This part is not clear: know that it was called from/as actionX, so it knows that if actionX consumes role needDB, it will need to get a database handler to pass it to run, etc.

3. Call actionX->run() passing the data object and any handler obtained at step 2.

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I tried using both run() and __PACKAGE__->run() in abstractAction.pm, but it calls the superclass method, not the child's. Is there any way I can know the child's package name from the parent? That doesn't even sound good. Is there a better way to do what I am trying to achieve?

I know I could simply do perl abstractAction.pm actionX arguments instead of perl actionX.pm arguments and call it a day, but I'd rather not.

Answer 1

Fundamentally, you'll need to call run as a method, using the name of the child class (if it's a class method) or an object of the child class (if it's an instance method) as the invocant.

Calling run as a class method:

ActionX->run(...)

Calling run as an instance method:

ActionX->new(...)->run(...)

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The other issue is that you're executing a .pm file, which leads to problems. Load modules, don't execute them. For example,

#!/usr/bin/perl
use strict;
use warnings;

my $action = shift(@ARGV)
   or die("usage\n");

$action =~ /^\w+\z/
   or die("Bad action\n");

my $pkg = $action;   # Or: my $pkg = "...::" . $action;

my $module =~ s{::}{/}g . '.pm';
require $module;

$pkg->new(@ARGV)->run();

If the script is named action, then you can do

action ActionX parameters