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comp.lang.ruby

accessor methods for class methods

Jason

9/5/2008 7:37:00 PM

It seems odd that cattr_* (i.e. cattr_accessor, cattr_reader,
cattr_writer) is not in the native Ruby and that you have to require
active support and rubygems to get this to work. Including the rails
stuff appears to slow things down a little. Why is this not built in the
native Ruby source?
--
Posted via http://www.ruby-....
5 Answers

Iñaki Baz Castillo

9/5/2008 7:49:00 PM

0

El Viernes, 5 de Septiembre de 2008, Jason Lillywhite escribi=C3=B3:
> It seems odd that cattr_* (i.e. cattr_accessor, cattr_reader,
> cattr_writer) is not in the native Ruby and that you have to require
> active support and rubygems to get this to work. Including the rails
> stuff appears to slow things down a little. Why is this not built in the
> native Ruby source?

Note that you can do the same using:

=2D-----------
class MyClass
=09
class << self
attr_accessor :class_attribute_1, :class_attribute_2
end

end
=2D----------


So you can use it:

=2D---------
MyClass.class_attribute_1 =3D something
=2D--------

=2D-=20
I=C3=B1aki Baz Castillo

David A. Black

9/5/2008 7:54:00 PM

0

Hi --

On Sat, 6 Sep 2008, Jason Lillywhite wrote:

> It seems odd that cattr_* (i.e. cattr_accessor, cattr_reader,
> cattr_writer) is not in the native Ruby and that you have to require
> active support and rubygems to get this to work. Including the rails
> stuff appears to slow things down a little. Why is this not built in the
> native Ruby source?

I can't answer that directly, but I can tell you why I'm glad it
isn't. It's partly that class variables are a bit oddball to start
with, and I'm not eager to see them used a lot more. But it's also the
terminology.

An "attribute" is, or should be, an attribute of an object. But class
variables are not object-specific; they're very promiscuous, visible
to a class, its instances, and all the subclasses and all their
instances.

Therefore, a class variable is not an appropriate choice for
representing an "attribute". The fit between instance variables, as a
language-level construct, and "attribute", as a concept, is very good;
but class variables are very different from instance variables, and
the "attr" terminology is very loose. (The methods may have uses, but
the names are problematic.)


David

--
Rails training from David A. Black and Ruby Power and Light:
Intro to Ruby on Rails January 12-15 Fort Lauderdale, FL
Advancing with Rails January 19-22 Fort Lauderdale, FL *
* Co-taught with Patrick Ewing!
See http://www.r... for details and updates!

Marc Heiler

9/5/2008 10:21:00 PM

0

> It seems odd that cattr_* (i.e. cattr_accessor, cattr_reader,
> cattr_writer) is not in the native Ruby

I can not answer this but personally I have stopped using class
variables after
- i had a smallish bug which was caused by a stupid usage I did long ago
of a class variable
- there really is not a huge need to use a class var in the first place
(in my opinion and experience).

So personally, for me, I have found that I can live perfectly happy
without class vars, and in these times, whenever I can achieve the same
with a very simple easy route, I use it. There may be a few valid use
cases for a class var but I honestly have never seen them as being very
important.
--
Posted via http://www.ruby-....

Jason

9/5/2008 11:00:00 PM

0


Thanks. That makes sense. I want to do what is simplest, but it seems
without cattr things would get worse. Here is what I'm trying to do:

I have one rb file used for inputs:

require 'rubygems'
require 'activesupport'
class Input
cattr_reader :y
def self.y
@y = 2
end
end

**except I have lots of vars instead of just :y and I'm assigning them
values here.

Then I go to a new rb file and do this:

require 'firstfile.rb'
class NewClass
def do_something
Input.y * 2.3
end
end

new = NewClass.new
p new.do_something

**The fact that I need to say "Input.y" seems very bulky. Is there a
better way to do this? Plus, if I get away from class vars, it will get
bulkier. any ideas?
--
Posted via http://www.ruby-....

David A. Black

9/5/2008 11:12:00 PM

0

HI --

On Sat, 6 Sep 2008, Jason Lillywhite wrote:

>
> Thanks. That makes sense. I want to do what is simplest, but it seems
> without cattr things would get worse. Here is what I'm trying to do:
>
> I have one rb file used for inputs:
>
> require 'rubygems'
> require 'activesupport'
> class Input
> cattr_reader :y
> def self.y
> @y = 2
> end
> end
>
> **except I have lots of vars instead of just :y and I'm assigning them
> values here.
>
> Then I go to a new rb file and do this:
>
> require 'firstfile.rb'
> class NewClass
> def do_something
> Input.y * 2.3
> end
> end
>
> new = NewClass.new
> p new.do_something
>
> **The fact that I need to say "Input.y" seems very bulky. Is there a
> better way to do this? Plus, if I get away from class vars, it will get
> bulkier. any ideas?

You're not actually using any class variables in your example. If you
delete the cattr_reader line, the code still runs. You're writing a
"reader" method (Input.y) by hand, and it's using an instance
variable, not a class variable (an instance variable belonging to the
class Input itself).


David

--
Rails training from David A. Black and Ruby Power and Light:
Intro to Ruby on Rails January 12-15 Fort Lauderdale, FL
Advancing with Rails January 19-22 Fort Lauderdale, FL *
* Co-taught with Patrick Ewing!
See http://www.r... for details and updates!