Question

I’m trying to be able to have a global exception capture where I can add extra information when an error happens. I have two classes, “crawler” and “amazon”. What I want to do is be able to call “crawl”, execute a function in amazon, and use the exception handling in the crawl function.

Here are the two classes I have:

require 'mechanize'

class Crawler
  Mechanize.html_parser = Nokogiri::HTML

  def initialize
    @agent = Mechanize.new
  end

  def crawl
    puts "crawling"

    begin
      #execute code in Amazon class here?
    rescue Exception => e
      puts "Exception: #{e.message}"
      puts "On url: #{@current_url}"
      puts e.backtrace
    end
  end

  def get(url)
    @current_url = url
    @agent.get(url)
  end
end

class Amazon < Crawler
  #some code with errors
  def stuff
    page = get("http://www.amazon.com")
    puts page.parser.xpath("//asldkfjasdlkj").first['href']
  end
end

a = Amazon.new
a.crawl

Is there a way I can call “stuff” inside of “crawl” so I can use that exception handling over the entire stuff function? Is there a better way to accomplish this?

EDIT:
This is when I ended up doing

require 'mechanize'

class Crawler
  Mechanize.html_parser = Nokogiri::HTML

  def initialize
    @agent = Mechanize.new
  end

  def crawl
    yield
  rescue Exception => e
    puts "Exception: #{e.message}"
    puts "On url: #{@current_url}"
    puts e.backtrace
  end

  def get(url)
    @current_url = url
    @agent.get(url)
  end
end

c = Crawler.new

c.crawl do
  page = c.get("http://www.amazon.com")
  puts page.parser.xpath("//asldkfjasdlkj").first['href']
end

Answer 1

You could have crawl accept a code block:

def crawl
  begin
    yield
  rescue Exception => e
    # handle exceptoin
  end
end

def stuff
  crawl do
    # implementation of stuff
  end
end

I’m not crazy about having a method with no body. A code block might make more sense here. May also eliminate the need for subclassing depending on what you want to do.