Getting brackets right, checking for package subs

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

Hi All,
I'm having a hard time getting my brackets right when checking if a subroutine is defined in another package. The problem is the name of the package and the sub are in a scalar called $package and a hash called %rmhash respectively.
I know I could just use eval but that feels like a cop out as I'm sure there is a way to do it just getting the brackets right, I've tried:-

defined &{ {$package}::$rmhash{$runmode} }
defined &{ ${$package}::{$rmhash{$runmode}} }
defined &{ ${ {$package}::{$rmhash{$runmode}} } }
defined &{ ${$package}::$rmhash{$runmode} }
[download]

All of which cause errors :(
Thanks for any help.

Lyle

Comment on Getting brackets right, checking for package subs Download Code

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Re: Getting brackets right, checking for package subs by Corion (Patriarch) on Feb 19, 2009 at 12:46 UTC
It would help us to help you better if you told us, exactly what errors you get in which case. Personally, I always use the following snippet to handle symbolic references: `no strict 'refs'; defined &{ "$package\::$subname" }` [download] but as I see that you're using a variable named `$runmode`, I get the feeling that you'd be better served by a simple dispatch table, especially as that brings you some more security: `my %runmodes = ( init => \&init, login => \&login, ... );` [download]	[reply] [d/l] [select]
Re^2: Getting brackets right, checking for package subs by cosmicperl (Chaplain) on Feb 19, 2009 at 13:27 UTC
Ahh brilliant. Thanks. I've adapted this a little and ended up with:- `defined &{ "${package}::$rmhash{$runmode}" }` [download] Which works with strict ref turned on. I would use a dispatch table, but that runmode hash is from CGI::Application. Lyle	[reply] [d/l]