Beefy Boxes and Bandwidth Generously Provided by pair Networks
Don't ask to ask, just ask

Importing methods and configuration at the same time?

by PopeFelix (Beadle)
on Aug 29, 2013 at 17:25 UTC ( #1051486=perlquestion: print w/replies, xml ) Need Help??
PopeFelix has asked for the wisdom of the Perl Monks concerning the following question:

Suppose I want to do the following:

use MyModule 'foo' => 'bar', qw/do_something do_something_else/;

So I want to:

  • Set the global configuration value foo to 'bar'
  • import the class methods do_something and do_something_else into my namespace

Assume for this example that I don't need to be able to specify the value for foo at runtime.

I can define MyModule like so:
package MyModule; our @EXPORT_OK = qw/do_something do_something_else/; my $FOO; sub import { my ($class, %config) = @_; $FOO = $config{'foo'}; } sub do_something { if ($FOO eq 'foo') { # do something here } else { # do something else } } sub do_something_else { if ($FOO eq 'foo') { # do something else here } else { # do something other than else } } 1;

But how would I then pass ('do_something', 'do_something_else') to Exporter?

Replies are listed 'Best First'.
Re: Importing methods and configuration at the same time?
by tobyink (Abbot) on Aug 29, 2013 at 17:37 UTC

    Put the config stuff into a hashref so that it doesn't get confused with symbols to be exported.

    use MyModule { foo' => 'bar' }, qw/do_something do_something_else/;

    Your import method would go something like this:

    sub import { my $class = shift; my $config = ref($_[0]) ? shift : {}; # do stuff with $config here unshift @_, $class; # restore $class onto @_ for Exporter goto \&Exporter::import; # need to use "goto" to ensure tail call }

    The alternative would be to use Exporter::TypeTiny which has a hook called _exporter_validate_opts exactly for doing this kind of thing...

    package MyModule; use strict; use warnings; use base 'Exporter::TypeTiny'; our @EXPORT_OK = qw( something something_else ); sub _exporter_validate_opts { my ($class, $config) = @_; # do stuff with $config here }

    Though it's worth noting that the $FOO variable here is basically a global. So if two different modules use your module, they will stomp on each others' config.

    Rather than using a global variable to store your config, it's better to use a lexical, and then export functions that close over that lexical. Sub::Exporter is generally the go-to module for doing that sort of thing; Exporter::TypeTiny can as well, but currently the interface for doing so is not as clean. (It's on my todo list.)

    use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://1051486]
Approved by sparkyichi
Front-paged by Corion
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others taking refuge in the Monastery: (1)
As of 2018-03-21 03:28 GMT
Find Nodes?
    Voting Booth?
    When I think of a mole I think of:

    Results (263 votes). Check out past polls.