From: Bob Hutchison <hutch-lists@...>
Date: 2010-03-01T00:30:58+09:00
Subject: Re: scope question


On 27-Feb-10, at 10:25 PM, Nick Brown wrote:

>> But it's generally considered good form to not use global variables  
>> in
>> the first place.  There's almost always a way to avoid using them.  
>> The
>> danger of using them is that if you use a global variable with your
>> code, and someone else uses a global variable of the same name in  
>> their
>> code, the two bits of code will both break if they are ever run
>> together.
>
> Raul: I believe it would also be bad form to hit the database
> unnecessarily with every pageview. If It's bad form to cache data in a
> variable that is visible to every page, then I don't want to be  
> good ;-)

But in that case you're writing a real Sinatra application not a toy :-)

>
> Is there a "better" way to do this than @@? Why do constants have
> different scopes than regular variables?


You can write your example as:

module Play
   class Application < Sinatra::Base

     vara = "foo"
     VARB = "bar"

     helpers do
       def geta
         vara
       end
       def getb
         VARB
       end
     end

     get '/a' do geta end
     get '/b' do getb end

   end
end


This should make thing a lot clearer as to what's going on, especially  
regarding scopes since it now looks more like actual Ruby code.

The constant VARB is really Play::Application::VARB in this case. If  
you want VARB global then you refer to it as ::VARB (everywhere)

In normal Ruby code what and where is vara in this case?

If you use @@vara it'll work, since vara will become a class variable  
of Play::Application

The trouble with that is that there's only one @@vara and it'll be  
used for all requests by all users. I'm also thinking that you  
probably don't really want that. If you don't then you'll have to keep  
vara someplace else, and look for it in each request.

Cheers,
Bob


> -- 
> Posted via http://www.ruby-forum.com/.
>

----
Bob Hutchison
Recursive Design Inc.
http://www.recursive.ca/
weblog: http://xampl.com/so