Class Help - Accessing Parent Methods from Child

ruby-talk
1

Hello everyone, I'm working on an API for Google Reader, and I'm having
some trouble with classes and inheritance and the like. I've got my main
class, Reader, and then two children classes, Subscription < Reader and
Item < Reader. Now, in my instance of Reader, I have two class variables
set: @headers, which are the headers that are to always be included in
the Net::HTTP call, and @connection, the Net::HTTP instance that is
connected to the Google Reader API.

I then have a method called get_page in Reader, which takes a URL and
any custom headers, then does the call. All this works perfectly well,
when #get_page is called from Reader. However, I also want to call
get_page from Subscription and Item. However, understandably, when I
call it from Subscription, I get an error that @connection and @headers
are undefined. I don't know where to start or what to do.

Any ideas?

Thanks,
Michael Boutros

···

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2

class Reader
  HEADERS = "<headers>"
  @@connection1 = "con1"
  @connection2 = "con2"
  class << self
    attr_reader :connection2
  end

  def do_things
    p HEADERS
    p @@connection1
    p self.class.connection2
  end
end

class Subscription < Reader
  def do_things
    p HEADERS
    p @@connection1
    p self.class.connection2
    p self.class.superclass.connection2
    p Reader.connection2
  end
end

Reader.new.do_things
#=> "<headers>"
#=> "con1"
#=> "con2"

Subscription.new.do_things
#=> "<headers>"
#=> "con1"
#=> nil
#=> "con2"
#=> "con2"

Conclusion: If you want to access class-level information from a
superclass, the simplest way is to use a constant (if the value is
constant). If the value needs to change, you can use a
@@class_variable (which is shared between the superclass and all its
descendants) or you can explicitly find the class you're interested in.

···

On Dec 2, 6:04 pm, Michael Boutros <m...@michaelboutros.com> wrote:

Hello everyone, I'm working on an API for Google Reader, and I'm having
some trouble with classes and inheritance and the like. I've got my main
class, Reader, and then two children classes, Subscription < Reader and
Item < Reader. Now, in my instance of Reader, I have two class variables
set: @headers, which are the headers that are to always be included in
the Net::HTTP call, and @connection, the Net::HTTP instance that is
connected to the Google Reader API.

I then have a method called get_page in Reader, which takes a URL and
any custom headers, then does the call. All this works perfectly well,
when #get_page is called from Reader. However, I also want to call
get_page from Subscription and Item. However, understandably, when I
call it from Subscription, I get an error that @connection and @headers
are undefined. I don't know where to start or what to do.

3

Hi --

···

On Mon, 3 Dec 2007, Michael Boutros wrote:

Hello everyone, I'm working on an API for Google Reader, and I'm having
some trouble with classes and inheritance and the like. I've got my main
class, Reader, and then two children classes, Subscription < Reader and
Item < Reader. Now, in my instance of Reader, I have two class variables
set: @headers, which are the headers that are to always be included in
the Net::HTTP call, and @connection, the Net::HTTP instance that is
connected to the Google Reader API.

I then have a method called get_page in Reader, which takes a URL and
any custom headers, then does the call. All this works perfectly well,
when #get_page is called from Reader. However, I also want to call
get_page from Subscription and Item. However, understandably, when I
call it from Subscription, I get an error that @connection and @headers
are undefined. I don't know where to start or what to do.

The variables you've mentioned (@headers and @connection) are instance
variables, not class variables. Class variables have two @@'s.

David

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