From: Rimantas Liubertas <rimantas@...>
Date: 2010-06-11T16:28:48+09:00
Subject: Re: case when and class

> I've found in case / when if the case is about a class :
>
> case my_var.class
> when String then puts my_var
> when Array  then my_var.each {|v| puts v}
> end
>
> doesn't work i do have to use :
>
> case my_var.class.to_s
> when 'String' then puts my_var
> when 'Array'  then my_var.each {|v| puts v}
> end
>
> why ?

"when" condition in case statement uses === to compare objects. For
strings a = b is true if a and b have the same characters, however
String === String is false:


>> a = "Hello"
=> "Hello"
>> b = "Hello"
=> "Hello"
>> a === b
=> true
>> String === String
=> false

BTW "===" is a method:

>> a.===(b)
=> true

so you can define your own rules when objects should be considered equal:

class Marble
  attr_accessor :size, :color

  def initialize(size, color)
    self.size = size
    self.color = color
  end

  def ===(other)
    self.color == other.color
  end

end

m1 = Marble.new(0.5, "red")
m2 = Marble.new(0.5, "green")
m3 = Marble.new(0.7, "red")

case m1
when m2
  puts "Matching marble is m2"
when m3
  puts "Matching marble is m3"
else
  puts "No match"
end

The result is "Matching marble is m3"

Regards,
Rimantas