From: Robert Klemme <shortcutter@...>
Date: 2010-02-04T17:15:14+09:00
Subject: Re: Dynamic Class Instance?

On 03.02.2010 20:13, Marnen Laibow-Koser wrote:
> Kale Davis wrote:
>> I am creating a Ruby script that basically:
>> 1) Has a prompt that gets a command string (ex. 'edit user1 15')
>> 2) Parses the string
>> 3) Runs specific command (like 'edit' or 'new')
>> 4) Repeats
>>
>> From a functional level I know how to make this work, but how do I make
>> it dynamic in the sense that another user could easily add their own
>> commands by adding a new subclass?
>>
>> I was thinking something like this:
>>
>> class Update < Command
>>   ...
>> end
>>
>> The problem is I don’t know how to dynamically create a new 'Update'
>> instance if that is the command string (ie 'update user')? I know how to
>> call a method using 'send' and I guess that would be another approach
>> maybe, but is there something for classes?
> 
> Classes are objects too.  They respond to Object#send.

For that he first needs the class instance.  Something like cl = 
Object.const_get("Update") will do.  Then you can do whatever you want 
to do with it.  In this case all classes should probably share a common 
interface method, e.g.

class Command
   def execute(*args)
     raise "Not implemented"
   end
end

class Update < Command
   def execute(*a)
     ...
   end
end

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/