From: Brian Candler <b.candler@...>
Date: 2010-04-11T03:06:06+09:00
Subject: Re: global variable in ruby

Jesse Jurman wrote:
>>  $buffer = Array.new
> 
> While global variables are really nice, most programmers try not to use 
> them, as they cause a lot of errors in the long end, dealing with other 
> programs or add-ons. I try not to use Global Variables in my programs, 
> but when I do need to, I name them so specifically, that they can not be 
> confused with another program's global variables.
> 
> i.e.  $program_name_buffer00 = Array.new

If it's just that a number of methods want access to the same buffer, 
you probably want to put them in a class and use an instance variable.

class PageParser
  attr_reader :buffer

  def initialize(buffer = [])
    @buffer = buffer
  end

  def get_citations_from_page(data, start_point, end_point)
    citations = get_substring_within_inclusive(data, start_point, 
end_point)
    u_arr = getURLsFromPage('http://www.xxxx.com/', citations)
    u_arr.each { |t|
     if (!beginsWith(t[1],'http://www.xxxx.com//gp/reader'))
       @buffer.push t[0]+'%%%'+t[1]
     end
    }
  end

  def get_substring_within_inclusive
    ...
  end
end

parser = PageParser.new
parser.get_citations_from_page(...)
p parser.buffer

If you really want a single buffer which is global to the whole program, 
then I'd say an instance variable of a Class is the way to go, which 
avoids the global variable namespace problem.

class PageParser
  @buffer = []
  def self.buffer
    @buffer
  end
end

PageParser.buffer << "hello"
PageParser.buffer << "world"
p PageParser.buffer

In the above code, @buffer is an instance variable of the Class object, 
not of instances of class PageParser (since class PageParser is itself 
an object)
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