From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-12-05T18:55:55+09:00
Subject: Re: Class arguments (newbe question)

On Sat, Dec 5, 2009 at 10:17 AM, Panagiotis Atmatzidis
<atma@convalesco.org> wrote:
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> Hash: SHA1
>
> Hello to the list!
>
> I have the following code which prints the ip's from fail2ban.log and puts then in an array:
>
> - --------------------------
> class ReadIPs
>  attr_accessor :ip
>  def initialize(ip)
>    @ip = ip
>  end

When you define an initialize method that receives an argument, you
must pass an argument when you create an instance with new.

>
>  def ip(filename)
>    ips = []
>    File.read(filename).lines.to_a.each do |place|
>      sf = 0
>      while sfn = place.index(/(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)/,sf)
>        sf = sfn + 3
>        ips << $&
>      end
>    end
>      return ips
>  end
> end
>
> # print methods
>
> a = ReadIPs.new("/Users/atma/Projects/ZoneReport/log/fail2ban.log")
> puts a.ip("/Users/atma/Projects/ZoneReport/log/fail2ban.log")
>
> - ---------------------------------
>
> What I don't understand is why do I need to give the argument to the new instance of ReadIPs.new class. In my view the code should look like:
>
> a = ReadIPs.new
> puts a.ip("/Users/atma/Projects/ZoneReport/log/fail2ban.log")

Then you can remove the initialize method from the ReadIPs class. In
fact, if that's the only thing you are going to do, you don't even
need a to be an instance. You can have a class method instead, since
you are not maintaining state:

class ReadIPs
  def self.ip(filename)
  ...
  end
end

and call it like

ReadIPs.ip("/Users/atma/Projects/ZoneReport/log/fail2ban.log")

Another possibility is to maintain the calculated array of matched IPs
in an instance, so what I would do in that case is:

class ReadIPs
  attr_reader :ips

  def initialize file_name
    @ips = perform the algorithm to match the ips.
  end
end

and then you can do:

a = ReadIPs.new("/Users/atma/Projects/ZoneReport/log/fail2ban.log")

which will calculate the ips and store them in the instance variable.
Then you can call:

a.ips

which will return the stored array.

Hope this helps,

Jesus.