Class and inheritance. Inherit data

ruby-talk
1

Hi guys,

I have a problem inheriting data from the parent class to its
subclasses. My code is as followed:

class Environmental
  def initialize
    convert_yaml = YAML::load_file('nizam.yaml')
  end
  def display
    #convert_yaml = YAML::load_file('nizam.yaml')
  end
end

class EnergyManagement < Environmental
  def initialize(title)
    @title = title
  end
  def display
    #convert_yaml = YAML::load_file('nizam.yaml')
    convert_yaml["System"]["Environmental"]["children"][2]["children"]
<< @title

    File.open("nizam_out.yaml", "w"){|f| YAML.dump(convert_yaml, f)}
  end
end

class WasteManagement < Environmental
  def initialize(title)
    @title = title
  end
  def display
    #convert_yaml = YAML::load_file('nizam.yaml')
    convert_yaml["System"]["Environmental"]["children"][3]["children"]
<< @title
    File.open("nizam_out.yaml", "w"){|f| YAML.dump(convert_yaml, f)}
  end
end

I want to use 'convert_yaml' for its subclasses (EnergyManagement and
WasteManagement) but when i run my code, 'convert_yaml' is not
recognized in the subclasses.

undefined local variable or method `convert_yaml' for
#<EnergyManagement:0x261d0b0> (NameError)

The reason i use this inheritance is because i want to write on the same
yaml file if both subclasses were called. Before this, i use
convert_yaml on every subclass but i found out that the yaml output
("nizam_out.yaml") file was overwritten if i call both subclasses at the
same time. Sorry if my explanation quite confusing as i do not know how
to explain this more clearly. Any help would be great. Thanks in
advance.

Nizam

···

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2

Hi,

I have a problem inheriting data from the parent class to its
subclasses. My code is as followed:

class Environmental
   def initialize
     convert_yaml = YAML::load_file('nizam.yaml')
   end

You declare 'convert_yaml' as a local variable here. It 'disappears' as soon as the method is left.
Even an instance variables (@convert_yaml) would be invisible to subclasses. And every instance of this class or a subclass would have it's own copy of the YAML file. I don't known if you intend this.

If you want that every subclass has it's own copy of the YAML file, then one way to do this, would be to declare 'convert_yaml' as an instance variable.

def initialize
   @convert_yaml = YAML::load_file('nizam.yaml')
end

and add an accessor to it:

def concert_yaml
   @convert_yaml
end

An accessor is a method which gives access to an instance variable.
Then your following code should work.

class EnergyManagement< Environmental
   def initialize(title)
     @title = title
   end
   def display
     #convert_yaml = YAML::load_file('nizam.yaml')
     convert_yaml["System"]["Environmental"]["children"][2]["children"]
<< @title

     File.open("nizam_out.yaml", "w"){|f| YAML.dump(convert_yaml, f)}
   end
end

class WasteManagement< Environmental
   def initialize(title)
     @title = title
   end
   def display
     #convert_yaml = YAML::load_file('nizam.yaml')
     convert_yaml["System"]["Environmental"]["children"][3]["children"]
<< @title
     File.open("nizam_out.yaml", "w"){|f| YAML.dump(convert_yaml, f)}
   end
end

I want to use 'convert_yaml' for its subclasses (EnergyManagement and
WasteManagement) but when i run my code, 'convert_yaml' is not
recognized in the subclasses.

undefined local variable or method `convert_yaml' for
#<EnergyManagement:0x261d0b0> (NameError)

See comment above.

The reason i use this inheritance is because i want to write on the same
yaml file if both subclasses were called. Before this, i use
convert_yaml on every subclass but i found out that the yaml output
("nizam_out.yaml") file was overwritten if i call both subclasses at the
same time.

A common super class won't fix your problem. You have still the same behavior. I think what you want is one class instance variable for all subclasses. Or better, factor the file handling out into a single class and initialize WasteManagement and EnergyManagement with an instance of this new class.

Greetings

Waldemar

···

Am 31.01.2011 23:40, schrieb Kamarulnizam Rahim:

3

Hi waldemar,

Thanks for your post. Actually, i dont want every subclasses to has its
own yaml file because the purpose of my program is to produce a sole
yaml file, with all data (@title) from every subclasses included in that
file.

Btw, what do you meant by

'I think what you want is one class instance variable for all
subclasses' ?

can you show a simple example on that? One more thing, i saw on net
there is a way by using '@@xxxx' variable and that variable can be
called outside the class. Is it true?

Thanks!!

nizam

···

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Posted via http://www.ruby-forum.com/.

4

Hi,

Thanks for your post. Actually, i dont want every subclasses to has its
own yaml file because the purpose of my program is to produce a sole
yaml file, with all data (@title) from every subclasses included in that
file.

Btw, what do you meant by

'I think what you want is one class instance variable for all
subclasses' ?

Sorry, I meant a class variable (@@var).

can you show a simple example on that? One more thing, i saw on net
there is a way by using '@@xxxx' variable and that variable can be
called outside the class. Is it true?

class MyYaml

   @@yaml = nil

   def self.yaml
     if @@yaml.nil? then
  @@yaml = File.open(...)
     end
     @@yaml
   end

end

access the yaml file with: MyYaml.yaml

Greetings,

Waldemar

···

Am 01.02.2011 10:02, schrieb Kamarulnizam Rahim: