Is there a way to define per-module global variables? My best
approximation is the following
module Foo
@@x = 0
def do_something_on_x
@@x = …
end
def x
@@x
end
end
The drawbacks are that I haven’t found anything similar to
attr_reader/writer/… for instance variables.
If interested in the real use case here it is: I’ve defined a module
which include a set of common functionalities which need to deliver
messages with a given verbosity. I want to avoid to pass the verbosity
configuration to all the involved class and methods but I want to avoid
to use a global $verbosity variable since the setting should be limited
to all the functionalities implemented by my module.
Here is how I’m using the verbosity setting:
module Foo
@@verbosity = 0
def incr_verbosity
@@verbosity += 1
end
def verbosity
@@verbosity
end
end
I would love to write something like
module Foo
@@verbosity = 0
module_attr_reader :verbosity
def incr_verbosity
@@verbosity += 1
end
end
Am I using the wrong tool for my end?
Many thanks in advance,
Cheers.
On Mon, Jan 22, 2007 at 02:52:58AM +0900, Trans wrote:
Am I using the wrong tool for my end?
Try a constant.
Already tried. I can’t stand the warning and I can’t blame the compiler
for outputting it: a constant would definitely be the wrong tool 
On 1/21/07, Stefano Z. [email protected] wrote:
On Mon, Jan 22, 2007 at 02:52:58AM +0900, Trans wrote:
Am I using the wrong tool for my end?
Try a constant.
Already tried. I can’t stand the warning and I can’t blame the compiler
for outputting it: a constant would definitely be the wrong tool 
why do you need this in your module? Is it going to be mixed into
something or no?
On Mon, 2007-01-22 at 03:05 +0900, Gregory B. wrote:
something or no?
end
foo
=> 50
=> 70
d.banana
=> 80
A.bar
=> 70
Well just a stolen idea from somewhere. But why not use module instance
variables:
module A
@foo = “Bar”
class << self; attr_accessor :foo; end
end
p A.foo
PS : Sometimes I really need to think hard to differentiate between a
class and a module.
On 1/21/07, Gregory B. [email protected] wrote:
On 1/21/07, Stefano Z. [email protected] wrote:
On Mon, Jan 22, 2007 at 02:52:58AM +0900, Trans wrote:
Am I using the wrong tool for my end?
Try a constant.
Already tried. I can’t stand the warning and I can’t blame the compiler
for outputting it: a constant would definitely be the wrong tool
why do you need this in your module? Is it going to be mixed into
something or no?
Something like this might work:
end
end
=> nil
A.bar = 20
=> 20
class B
include A
def apple
foo
end
end
=> nil
c = B.new
=> #<B:0x31485c>
c.apple
=> 30
c.apple
=> 40
c.apple
=> 50
class C
include A
def banana
foo + 10
end
end
=> nil
d = C.new
=> #<C:0x1cc1b4>
d.banana
=> 70
d.banana
=> 80
A.bar
=> 70
On 1/21/07, Hemant K. [email protected] wrote:
module A
@foo = “Bar”
class << self; attr_accessor :foo; end
end
p A.foo
That’s probably the same effect, and a little shorter, too.
PS : Sometimes I really need to think hard to differentiate between a
class and a module.
Maybe you’d find this post interesting: O'Reilly Media - Technology and Business Training
Not exactly the same topic, but related
On Mon, 2007-01-22 at 04:21 +0900, Gregory B. wrote:
And i missed that, you will have to use self.class.foo to access the
module instance variable from instance methods.
PS : Sometimes I really need to think hard to differentiate between a
class and a module.
Maybe you’d find this post interesting: O'Reilly Media - Technology and Business Training
Not exactly the same topic, but related
PS: hmm thanks.
On Mon, Jan 22, 2007 at 03:00:09AM +0900, Gregory B. wrote:
why do you need this in your module? Is it going to be mixed into
something or no?
Actually no. It’s just the “namespace” in which I’m implementing various
classes.
I can alternatively write a class pertaining to this namespace and use a
class variable of that class, but since the class would be otherwise
pointless I thought a module variable would have been a better solution
…
Cheers.
On Mon, Jan 22, 2007 at 04:08:38AM +0900, Hemant K. wrote:
Well just a stolen idea from somewhere. But why not use module instance
variables:
Thanks (to you and Gregor), that’s precisely what I was looking for!
I also found the same example in the pickaxe book (in which sometime
it’s difficult to find what you were looking for from the index …),
and now I’ve a clearer understanding of its meaning.
Cheers.
On Mon, Jan 22, 2007 at 10:07:54AM +0900, Mike K. wrote:
I also found the same example in the pickaxe book (in which sometime
it’s difficult to find what you were looking for from the index …),
and now I’ve a clearer understanding of its meaning.
Where is this discussed in pickaxe (which page number)?
Page 374.
Note that the discussed topic is not “module instance variables”, but
rather the class << self trick for associating a class with the self
object (which in the pickaxe case is a class object). AFAIU the same is
done in the solution proposed to me, but with a module object instead of
a class object.
Correct me if my understanding is wrong.
Cheers.
On Mon, Jan 22, 2007 at 08:29:24AM +0900, Stefano Z. wrote:
I also found the same example in the pickaxe book (in which sometime
it’s difficult to find what you were looking for from the index …),
and now I’ve a clearer understanding of its meaning.
Where is this discussed in pickaxe (which page number)?
I ran into basically the same issue a few weeks ago and came up with the
same solution. I read the pickaxe cover to cover (a long time ago) and
I couldn’t remember seeing that particular example. On the other hand,
much of what I read I’m forgetting.
On Mon, Jan 22, 2007 at 05:11:49PM +0900, Stefano Z. wrote:
Where is this discussed in pickaxe (which page number)?
Page 374.
Hmm, must be first edition, although you gave me a clue where to look
for it. In the second edition, it’s under “Class Instance Variables” in
Chapter 24: Classes and Objects, page 388.
Yeah, I guess I just don’t recall reading that the first time.
Thanks.
On Tue, 23 Jan 2007 14:05:59 +0900, Mike K. wrote:
On Mon, Jan 22, 2007 at 05:11:49PM +0900, Stefano Z. wrote:
Where is this discussed in pickaxe (which page number)?
Page 374.
Hmm, must be first edition, although you gave me a clue where to look
for it. In the second edition, it’s under “Class Instance Variables” in
Chapter 24: Classes and Objects, page 388.
Uhm my fault. It’s actually the second edition, but indeed I wanted to
point to the page you’re mentioning. I probably screwed up the page
numbers between the “paper” page numbers and the pdf page numbers I was
looking at. Or something similar, since right now even the pdf page
number does not much … But it’s cool, we both found what we were
looking for
Cheers.