From: "Iñaki Baz Castillo" <ibc@...>
Date: 2011-05-01T21:36:42+09:00
Subject: Re: Why defining a constant in a method is not allowed but using self.class.const_set is allowed?

2011/5/1 Robert Klemme <shortcutter@googlemail.com>:
>> Humm, yes, having a HASH constant containing a hash is faster than
>> accessing instance variables within a class. Just a bit, but faster :)
>
> You never mentioned a performance problem you are trying to solve. Could be
> that you are worrying too much about an irrelevant detail.

Yes, I know :)
Yoo much-preoptimization :)


>> So I'll use it, something like:
>>
>> module MyApp
>>   CONFIGURATION = {}
>> end
>
> This might be a corner case but I would generally advice to not use global
> variables (or constants) for this.  The reason is simply that you loose a
> lot of flexibility.  You can only ever have one active configuration at a
> time - and you cannot change it concurrently as well.

Well, I can change it globaly:


H1 = {:qwe=>123}

H1.object_id
=> 21460540

h2 = {:asd=>999}

H1.replace h2

H1
=> {:asd=>999}

H1.object_id
21460540


:)




> It may be OK for a small script or application but if you make that design a
> habit you might run into problems later.  Generally it is better to provide
> configuration and other information from the outside because that also makes
> testing easier.  You can pass in whatever mock you want to use to test a
> particular feature.  If OTOH instances decide themselves where to get the
> information from (i.e. the global variable / constant) you are out of luck
> (or you need to patch methods of the class under test while testing which is
> generally not a good idea because then you don't test any more what will be
> productive eventually).

I read the configuration from a text file (maybe YAML). But later, for
each request in my server, my classes and methods must access some
configuration fields (for each request), for example the log level.
This is the reason I need such access to be as fast as possible.

Anyhow, I don't want to loose flexibility neither mantain ugly code
(deleting and re-creating constants for each configuration change).
After this thread I hope that using a constant hash (i.e:
MyServer::CONFIGURATION) is a good choice between
ellegancy/flexibility and efficience.


Thanks a lot for your response.




-- 
Iñaki Baz Castillo
<ibc@aliax.net>