Question

I’m sure this is covered in the documentation somewhere but I have been unable to find it… I’m looking for the syntactic sugar that will make it possible to call a method on a class whose name is stored in a hash (as opposed to a simple scalar):

use strict; use warnings;

package Foo;
sub foo { print "in foo()\n" }

package main;
my %hash = (func => 'foo');

Foo->$hash{func};

If I copy $hash{func} into a scalar variable first, then I can call Foo->$func just fine… but what is missing to enable Foo->$hash{func} to work?

(EDIT: I don’t mean to do anything special by calling a method on class Foo — this could just as easily be a blessed object (and in my actual code it is); it was just easier to write up a self-contained example using a class method.)

EDIT 2: Just for completeness re the comments below, this is what I’m actually doing (this is in a library of Moose attribute sugar, created with Moose::Exporter):

# adds an accessor to a sibling module
sub foreignTable
{
    my ($meta, $table, %args) = @_;

    my $class = 'MyApp::Dir1::Dir2::' . $table;
    my $dbAccessor = lcfirst $table;

    eval "require $class" or do { die "Can't load $class: $@" };

    $meta->add_attribute(
        $table,
        is => 'ro',
        isa => $class,
        init_arg => undef,  # don't allow in constructor
        lazy => 1,
        predicate => 'has_' . $table,
        default => sub {
            my $this = shift;
            $this->debug("in builder for $class");

            ### here's the line that uses a hash value as the method name
            my @args = ($args{primaryKey} => $this->${\$args{primaryKey}});
            push @args, ( _dbObject => $this->_dbObject->$dbAccessor )
                if $args{fkRelationshipExists};

            $this->debug("passing these values to $class -> new: @args");
            $class->new(@args);
        },
    );
}

I’ve replaced the marked line above with this:

        my $pk_accessor = $this->meta->find_attribute_by_name($args{primaryKey})->get_read_method_ref;
        my @args = ($args{primaryKey} => $this->$pk_accessor);

PS. I’ve just noticed that this same technique (using the Moose meta class to look up the coderef rather than assuming its naming convention) cannot also be used for predicates, as Class::MOP::Attribute does not have a similar get_predicate_method_ref accessor. 🙁

Answer 1

Foo->${\$hash{func}};

But for clarity, I’d probably still write it as:

my $method = $hash{func};
Foo->$method;