Class variable weirdness

Ruby
1

I was fooling around with class variables tonight, and I know this is
pretty silly, but forsome reason this code will work when in
its own class, as you can see in class A and class B, but when I
put the code together into class C I get an error

class_vars.rb:26: undefined method `up=’ for C:Class (NoMethodError)

Can anyone explain why this is happening?

class A
@@foo=1
def self.foo=(n)
@@foo = n
end
end
#prints “10”
puts “%s” % A.foo=10

class B
@@foo=1
def self.up
@@foo+=1
end
end
#prints “2”
puts “%s” % B.up

class C
@@foo=1
def self.foo=(n)
@@foo = n
end
def self.up
@@foo+=1
end
end
#should print “2, 10” but it doesn’t work for me.
puts “%s, %s” % (C.up,C.foo=10)

2

Hi –

On Thu, 26 Jan 2006, Alex C. wrote:

I was fooling around with class variables tonight, and I know this is
pretty silly, but forsome reason this code will work when in
its own class, as you can see in class A and class B, but when I
put the code together into class C I get an error

class_vars.rb:26: undefined method `up=’ for C:Class (NoMethodError)

Can anyone explain why this is happening?
[…]
puts “%s, %s” % (C.up,C.foo=10)

You need an array there: [C.up, C.foo=10]. The way you’ve got it,
what’s happening is that it’s being parsed as two assignments:

C.up = 10
C.foo = nil

David

–
David A. Black
[email protected]

“Ruby for Rails”, from Manning Publications, coming May 1, 2006!

3

hi David

On 1/25/06, [email protected] [email protected] wrote:

Can anyone explain why this is happening?
[…]
puts “%s, %s” % (C.up,C.foo=10)

You need an array there: [C.up, C.foo=10]. The way you’ve got it,
what’s happening is that it’s being parsed as two assignments:

C.up = 10
C.foo = nil

Thanks I appreciate the quick reply, I think the () was a bit of
python showing its roots.
What I would like to do now is get instances of those classes and use
the
methods that I’ve defined but I cant figure out how, without changing
the class.

class A
@@foo=1
def self.foo=(n)
@@foo = n
end
end
puts “%s” % A.foo=10
a = A.new
#this does not work for an instance
#puts “%s” % a.foo=10

4

Hi–

On Thu, 26 Jan 2006, Alex C. wrote:

C.up = 10
def self.foo=(n)
@@foo = n
end
end
puts “%s” % A.foo=10
a = A.new
#this does not work for an instance
#puts “%s” % a.foo=10

Instances of A don’t have a foo method, so you would indeed have to
change the class to give them one. Is there a reason you don’t want
to in this particular case?

David

–
David A. Black
[email protected]

“Ruby for Rails”, from Manning Publications, coming May 1, 2006!

5

Instances of A don’t have a foo method, so you would indeed have to
change the class to give them one. Is there a reason you don’t want
to in this particular case?

Yes I see I can not have it both ways now, either a class.method or a
instance.method
but not both with the same declairation.
Thanks David