From: Panagiotis Atmatzidis <atma@...>
Date: 2009-12-05T19:12:01+09:00
Subject: Re: Class arguments (newbe question)


On 05 Δεκ 2009, at 11:55 π.μ., Jesús Gabriel y Galán wrote:

> On Sat, Dec 5, 2009 at 10:17 AM, Panagiotis Atmatzidis
> <atma@convalesco.org> wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> 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,

It helped a lot! Thank you for the prompt & detailed answer


Panagiotis (atmosx) Atmatzidis

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