[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

Best way to get a class object from its name?

Wes Gamble

2/22/2007 9:22:00 PM

All,

In my Rails app., I'm doing something like this:

eval("#{requested_controller_class}.respond_to?('session_data_not_needed_by?')")

where requested_controller_class is the name of an existing (controller)
class.

Is the above code the best of way of invoking respond_to? on the class
in question, or is there some better way to get the actual class object
based solely on it's name?

Thanks,
Wes

--
Posted via http://www.ruby-....
3 Answers

Ezra Zygmuntowicz

2/22/2007 9:35:00 PM

0

Hi~

On Feb 22, 2007, at 1:21 PM, Wes Gamble wrote:

> All,
>
> In my Rails app., I'm doing something like this:
>
> eval("#{requested_controller_class}.respond_to?
> ('session_data_not_needed_by?')")
>
> where requested_controller_class is the name of an existing
> (controller)
> class.
>
> Is the above code the best of way of invoking respond_to? on the class
> in question, or is there some better way to get the actual class
> object
> based solely on it's name?
>
> Thanks,
> Wes


Since you are in a Rails app the better way of doing that would be
like this:

requested_controller_class.constantize.respond_to? :session_data_not_nee
ded_by?


Cheers-
-- Ezra Zygmuntowicz
-- Lead Rails Evangelist
-- ez@engineyard.com
-- Engine Yard, Serious Rails Hosting
-- (866) 518-YARD (9273)

Chris Shea

2/22/2007 9:37:00 PM

0

On Feb 22, 2:21 pm, Wes Gamble <w...@att.net> wrote:
> All,
>
> In my Rails app., I'm doing something like this:
>
> eval("#{requested_controller_class}.respond_to?('session_data_not_needed_by?')")
>
> where requested_controller_class is the name of an existing (controller)
> class.
>
> Is the above code the best of way of invoking respond_to? on the class
> in question, or is there some better way to get the actual class object
> based solely on it's name?
>
> Thanks,
> Wes
>
> --
> Posted viahttp://www.ruby-....

Getting class objects was one of the problems in Ruby Quiz #113. See:
http://www.ruby-...topic/97203 or
http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/90223b4...

There are a couple of solutions given. Assuming your class name is in
the variable named 'quiz' this (from James II) does it:
quiz.split("::").inject(Object) { |par, const| par.const_get(const) }

Ben Bleything

2/22/2007 9:41:00 PM

0

On Fri, Feb 23, 2007, Wes Gamble wrote:
> eval("#{requested_controller_class}.respond_to?('session_data_not_needed_by?')")
>
> where requested_controller_class is the name of an existing (controller)
> class.
>
> Is the above code the best of way of invoking respond_to? on the class
> in question, or is there some better way to get the actual class object
> based solely on it's name?

>> str = "ActiveRecord::Base"
=> "ActiveRecord::Base"
>> str.constantize.respond_to? :new
=> true

String#constantize is provided by Rails someplace. In non-Rails Ruby
code, you could do this:

>> Module.const_get( 'ActiveRecord' ).const_get( 'Base' ).respond_to?
>> :find
=> true

Of course, if it's a single-level, you only need one of those.

Cheers,
Ben