From: lasitha <lasitha.ranatunga@...>
Date: 2009-02-25T16:10:04+09:00
Subject: Re: Extrange String#=~ behaviour

On Wed, Feb 25, 2009 at 8:05 AM, 7stud -- <bbxx789_05ss@yahoo.com> wrote:
> Iñaki Baz Castillo wrote:
>> Hi, I can't understand it:
>>
>>   class String
>>     def =~ obj
>>       puts "Sorry, I don't compare"
>>     end
>>   end
>>
>> b) ¿?
>> irb> "string" =~ /string/
>> 0
>>

Turns out using Regexp.new behaves as expected:

07> "string" =~ Regexp.new('string')
Sorry, I don't compare
--> nil

> class Regexp
>  def =~(obj)
>    puts "goodbye"
>  end
> end
>
> puts /string/ =~ "string"  #0

In this case too:

08> Regexp.new('string') =~ "string"
goodbye
--> nil

Ruby 1.9 rdoc for Regexp#=~ hints at special treatment for regexp literals [1]:
"This assignment is implemented in the Ruby parser. So a regexp
literal is required for the assignment. The assignment is not occur if
the regexp is not a literal."
But that is in the context of assigning to ?<var> type named captures
within a regexp on the LHS, so i don't know if it's relevant.

Hope someone who knows the implementation can shed more light.

Cheers,
lasitha.

[1] http://ruby-doc.org/core-1.9/classes/Regexp.html#M001214