# Why catch block directly exeute **URL:** \ **Category:** ruby-talk\ **Created:** [7 December 2010 10:08 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072 "2010-12-07T10:08:38Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Durga\_B](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@Durga\_B](https://rubytalk.org/u/Durga_B)\ **Post date:** [7 December 2010 10:08 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072/1 "2010-12-07T10:08:38Z")
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. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Jesus\_Gabriel\_y\_Gala](https://avatars.discourse-cdn.com/v4/letter/j/96bed5/32.png) [@Jesus\_Gabriel\_y\_Gala](https://rubytalk.org/u/Jesus_Gabriel_y_Gala)\ **Post date:** [7 December 2010 10:27 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072/2 "2010-12-07T10:27:17Z")
[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.catch) [http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref\_m\_kernel.html#Kernel.throw](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. > **···** > > On Tue, Dec 7, 2010 at 11:08 AM, Durga B. \ 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. ---
**Author:** ![flebber](https://avatars.discourse-cdn.com/v4/letter/f/f9ae1b/32.png) [@flebber](https://rubytalk.org/u/flebber)\ **Post date:** [7 December 2010 10:55 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072/3 "2010-12-07T10:55:17Z")
[http://ruby.activeventure.com/programmingruby/book/tut\_exceptions.html](http://ruby.activeventure.com/programmingruby/book/tut_exceptions.html) [http://ruby-doc.org/core/classes/Exception.html](http://ruby-doc.org/core/classes/Exception.html) > > **···** > > On Dec 7, 9:08 pm, "Durga B." \ 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. > > > > -- > > Posted viahttp://www.ruby-forum.com/. ---
**Author:** ![Durga\_B](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@Durga\_B](https://rubytalk.org/u/Durga_B)\ **Post date:** [7 December 2010 10:35 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072/4 "2010-12-07T10:35:08Z")
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. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Jesus\_Gabriel\_y\_Gala](https://avatars.discourse-cdn.com/v4/letter/j/96bed5/32.png) [@Jesus\_Gabriel\_y\_Gala](https://rubytalk.org/u/Jesus_Gabriel_y_Gala)\ **Post date:** [7 December 2010 10:57 UTC](https://rubytalk.org/t/why-catch-block-directly-exeute/61072/5 "2010-12-07T10:57:35Z")
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 [Exceptions, Catch, and Throw](http://phrogz.net/programmingruby/tut_exceptions.html%5C)) : 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. > **···** > > On Tue, Dec 7, 2010 at 11:35 AM, Durga B. \ 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.