Class+object vars

ruby-talk
1

Hello,

What is this @x ?
Wondering why that is allowed --
@objectvar of class is not the same as @@classvar of objects...

class A
  @x=1
  def A.b; @x+=1; end
end
p A.b

How can a class best being initalized?

class A
  def self.initialize; p "started" end
end
# How to start it? (don't want to explicitely call A.initialize) ?

Thanks Berg

2

Hi Berg,

"A class variable (@@) is shared among the class and all of its
descendants. A class instance variable (@) is not shared by the class's
descendants."

There's a trend of using (class) instance variables most of the time and to
use class variables _only_ when you really need to share state between
descendants.

I didn't understand the "initialization" part.
Could you give one example where you would like to do so?

Best regards,
Abinoam Jr.

···

On Fri, May 20, 2016 at 10:16 PM, A Berger <aberger7890@gmail.com> wrote:

Hello,

What is this @x ?
Wondering why that is allowed --
@objectvar of class is not the same as @@classvar of objects...

class A
  @x=1
  def A.b; @x+=1; end
end
p A.b

How can a class best being initalized?

class A
  def self.initialize; p "started" end
end
# How to start it? (don't want to explicitely call A.initialize) ?

Thanks Berg

Unsubscribe: <mailto:ruby-talk-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-talk&gt;

3

Hi,
thanks for yout answer

Hi Berg,

"A class variable (@@) is shared among the class and all of its

descendants. A class instance variable (@) is not shared by the class's
descendants."

Thats why I'm asking how @x is behaving inside a class (as in example) -
where is it stored? Which variable is this of? (Why no error?)

I didn't understand the "initialization" part.
Could you give one example where you would like to do so?

For an object we call X.new
to run the #initialize() ,
what can be done to run .initialize of a class ?

Thx Berg

···

Am 21.05.2016 05:20 schrieb "Abinoam Jr." <abinoam@gmail.com>:

Best regards,
Abinoam Jr.

On Fri, May 20, 2016 at 10:16 PM, A Berger <aberger7890@gmail.com> wrote:

Hello,

What is this @x ?
Wondering why that is allowed --
@objectvar of class is not the same as @@classvar of objects...

class A
  @x=1
  def A.b; @x+=1; end
end
p A.b

How can a class best being initalized?

class A
  def self.initialize; p "started" end
end
# How to start it? (don't want to explicitely call A.initialize) ?

Thanks Berg

Unsubscribe: <mailto:ruby-talk-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-talk&gt;

4

Thats why I'm asking how @x is behaving inside a class (as in example) -
where is it stored? Which variable is this of? (Why no error?)

If you do `@var = value` then you always set the instance variable `@var`
on the object referenced by `self`. In the class body `self` references the
class object.

class Person
  @count = 0
end
Person.instance_variable_get("@count") # => 0

For an object we call X.new
to run the #initialize() ,
what can be done to run .initialize of a class ?

`#initialize` is called by `.new`. If you want to initialize class instance
variables then I'd do it in the body. There's no class-level `.initialize`
that'd be called automatically as there's no need for one. When you define
a class then you do have an object you want to initialize. When you define
`#initialize` there's still no object to initialize: you first define the
class and then use the class to create instances.

···

--
Greg Navis
I help tech companies to scale Heroku-hosted Rails apps.
Free, biweekly scalability newsletter for SaaS CEOs
<http://www.gregnavis.com/newsletter/&gt;

5

Hi
Super fast answer :slight_smile:
How can I distinguish to call / dont call such '.initialize' (for B) if
building a subclass A<B ?

Thx Berg

···

Unsubscribe: <mailto:ruby-talk-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-talk&gt;

6

Hi
Super fast answer :slight_smile:

Corr:

How can I accomplish to call / dont call such '(self).initialize'/body

(for B, C,...) if building a subclass A<B, B < C ?
- metaprogramming only??

Thx Berg

>
> Unsubscribe: <mailto:ruby-talk-request@ruby-lang.org

?subject=unsubscribe>

···

Am 21.05.2016 10:52 schrieb "A Berger" <aberger7890@gmail.com>:

> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-talk&gt;
>