Hello!
Forgive my newbie-ness.
Using ruby 1.8, while trying to create a similar example of
one I found to the book called “The Ruby Way”:
class Foo
@@bar = 10
end
Foo.bar = 4
I get:
elathan@velka:~/src/ruby> ruby test.rb
test.rb:7: undefined method `bar=’ for Foo:Class (NoMethodError)
Is this behaviour normal?
Enjoy,
–
University of Athens I bet the human brain
Physics Department is a kludge --Marvin Minsky
elathan@velka:~/src/ruby> ruby test.rb
test.rb:7: undefined method `bar=' for Foo:Class (NoMethodError)
Is this behaviour normal?
Yes, what you want is a class *instance* variable
svg% cat b.rb
#!/usr/bin/ruby
class A
class << self
attr_accessor :a
end
end
A.a = 12
p A.a
svg%
svg% b.rb
12
svg%
a class variable can be seen as a shared variable
svg% cat b.rb
#!/usr/bin/ruby
class A
@@a = 12
def self.a
p @@a
end
def a
p @@a
end
end
class B < A
def self.b
p @@a
end
def b
p @@a
end
end
A.a
A.new.a
B.b
B.new.b
svg%
svg% b.rb
12
12
12
12
svg%
Guy Decoux
Actually, I want an easy way to access a class variable from
another class. I construct objects, which I want them to
carry an array specific to their class:
class Foo
@@info = …
…
end
class Bar
@@info = …
…
end
As I see from your reply, the only way to access a class
variable from another class (or outside the class in general)
is to define self.foo and foo methods; foo stands for the class
var.
This sounds a little bit wierd to me, since, in the book[*] I have,
the author accesses a class variable implicitly, without having
define self.foo and foo inside the class.
Thanks for your reply!
[*] The Ruby Way - Hal Fulton
Enjoy,
On Sun, Oct 12, 2003 at 09:21:24PM +0900, ts wrote:
elathan@velka:~/src/ruby> ruby test.rb
test.rb:7: undefined method `bar=’ for Foo:Class (NoMethodError)Is this behaviour normal?
Yes, what you want is a class instance variable
–
University of Athens I bet the human brain
Physics Department is a kludge --Marvin Minsky
Hi –
This sounds a little bit wierd to me, since, in the book[*] I have,
the author accesses a class variable implicitly, without having
define self.foo and foo inside the class.
Class variables are directly visible only down the class hierarchy:
class A
@@x = 1
end
class B < A
puts @@x # 1
end
You can give access to them, but you have to do it explicity:
class A
def self.peek # technically you don’t have to call it info 
@@info
end
def self.poke(x)
@@info = x
end
end
(This is similar to the kind of get/set methods that are often
implemented using instance variables, but the resemblance is
superficial. Class variables are a different creature, and therfore
not a drop-in replacement for instance variables.)
Just to try to get it all clear: do you have a page number in The Ruby
Way for the example you mentioned?
David
On Mon, 13 Oct 2003, Elias Athanasopoulos wrote:
–
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav
Yes. It’s on page 250.
As I see it now, the author has defined Metal.current_temp=(x).
I apologize for the confusion and I’m thankfull for your
detailed replies.
Now it’s all clear to me.
Enjoy,
On Mon, Oct 13, 2003 at 05:23:46AM +0900, dblack@superlink.net wrote:
Just to try to get it all clear: do you have a page number in The Ruby
Way for the example you mentioned?
–
University of Athens I bet the human brain
Physics Department is a kludge --Marvin Minsky