From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-12-07T19:57:35+09:00
Subject: Re: why catch block directly exeute

On Tue, Dec 7, 2010 at 11:35 AM, Durga B. <bdurgaprasad_nyros@yahoo.com> wrote:
> Thank you very much Jesús Gabriel y Galán but some confusion please
> explain with different catch and throw,not include same both are same
> block take as a different ,please.

I'm not sure I understand your question. The way it works is that when
you throw, Ruby looks up through the stack for a catch with the same
symbol. If it finds it, the block passed to catch is terminated
immediately, and the block returns the value passed to throw. This is
useful to exit from a deeply nested structure, for example (based on
http://phrogz.net/programmingruby/tut_exceptions.html) :

def processValue value
  throw :quit if value =~ /quit!/i
  value.downcase
end

def promptAndGet(prompt)
  print prompt
  value = gets.chomp
  processValue value
end

catch :quit do
  name = promptAndGet "Name: "
  age = promptAndGet "Age: "
  sex = promptAndGet "Sex: "
  #do_something_with name, age, sex
end

You can nest catch blocks:

catch(:first_level) do
  puts "at first level"
  catch(:second_level) do
    puts "At second level"
    if (rand(2) == 0)
      throw :second_level
    else
      throw :first_level
    end
    puts "still in second level"
  end
  puts "still in first level"
end

Jesus.