From: dblack@...
Date: 2007-07-24T19:10:22+09:00
Subject: Re: case equality question

Hi --

On Tue, 24 Jul 2007, Phil Meier wrote:

> Hello
>
> I do not understand the following code:
>
> ======
> file = File.open('test.txt', 'r')
> hash = {'file' => file, 'title' => 'title'}
> hash.map { | param_key, param_value |
>  puts "param_key = #{param_key}"
>  puts "param_value = #{param_value}"
>  puts "(param_value === String) = #{(param_value === String)}"
>  case param_value
>    when String
>      puts "This is a String!"
>    when File
>      puts "This is a File!"
>    else
>      puts "Neither String nor File!!!"
>  end
> }
> file.close
> ===
>
> When I run this code the output is as follows:
> param_key = title
> param_value = title
> (param_value === String) = false
> This is a String!
> param_key = file
> param_value = #<File:0x2b689b8>
> (param_value === String) = false
> This is a File!
>
> Why does Ruby goes to the when String case even if (param_value === String) 
> is false?

Because String === param_value is true :-)  That's how the case thing
works:

   obj = Object.new
   def obj.===(other)
     puts "I'm being cased!"
     true
   end

   case "blah"
     when obj
   end

Output:

   I'm being cased!

because obj === "blah" is being called.


David

-- 
* Books:
   RAILS ROUTING (new! http://www.awprofessional.com/title/0321509242)
   RUBY FOR RAILS (http://www.manning.com/black)
* Ruby/Rails training
     & consulting:  Ruby Power and Light, LLC (http://www.rubypal.com)