From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-12-07T19:27:17+09:00
Subject: Re: why catch block directly exeute

On Tue, Dec 7, 2010 at 11:08 AM, Durga B. <bdurgaprasad_nyros@yahoo.com> wrote:
> catch (:finish) do
>    puts "Generated 1000 random numbers without generating 123!"
>    end
>
> The above code if not throw or any thing call and execute directly .
> How is it works please any one explain and if possible give a example
> for throw and catch block.

http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_m_kernel.html#Kernel.catch
http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_m_kernel.html#Kernel.throw

It's how catch works. It executes the block. If within the block, the
symbol you pass to catch is thrown, catch returns the value passed to
throw (second argument or nil). If not thrown, catch terminates
normally, and returns the value of the last expression in the block:

value = catch(:finish) do
  [1,2,3,4].each do |v|
    throw(:finish,v) if v > 3
    puts v
  end
end

irb(main):019:0> value = catch(:finish) do
irb(main):020:1*   [1,2,3,4].each do |v|
irb(main):021:2*     throw(:finish, v) if v > 3
irb(main):022:2>     puts v
irb(main):023:2>   end
irb(main):024:1> end
1
2
3
=> 4

If not thrown:

irb(main):025:0> value = catch(:finish) do
irb(main):026:1*   [1,2,3,4].each do |v|
irb(main):027:2*     throw(:finish, v) if v > 10
irb(main):028:2>     puts v
irb(main):029:2>   end
irb(main):030:1> end
1
2
3
4
=> [1, 2, 3, 4]

Returns the full array, which is what the each method returns.

Jesus.

Jesus.