From: Robert Klemme <shortcutter@...>
Date: 2011-05-02T03:05:32+09:00
Subject: Re: Why defining a constant in a method is not allowed but using   self.class.const_set is allowed?

On 01.05.2011 14:36, Iņaki Baz Castillo wrote:
> 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 :)

Don't.  You know what Knuth said about it, do you?

>>> 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:

Of course.  But you need synchronization to make that thread safe.

>> 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.

Passing a configuration via a setter is not really something to worry 
about speed wise.

> 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.

Is your code loaded once or is it reloaded for every request?

> Thanks a lot for your response.

You're welcome!

Kind regards

	robert

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