From: "David A. Black" <dblack@...>
Date: 2005-08-03T20:22:44+09:00
Subject: Re: [RCR] array or with non-array

Hi --

On Wed, 3 Aug 2005, Eric Mahurin wrote:

> I think a primary example where I would really like real
> duck-typing in a built-in would be Regexp#match(str).  This
> requires the arg to be a String.  I would really like to have
> this be able to operate on a file.  If I implement a class that
> walks like, talks like, quacks like a String but really
> accesses a file (practically did that in my rubyforge cursor
> project), it wouldn't do any good because Regexp#match only
> takes a String - period.

You can define #to_str on your object to get Regexp#match to accept
it as an argument:

   irb(main):006:0> o = Object.new
   => #<Object:0x401f3db4>
   irb(main):007:0> def o.to_str; "hi"; end
   => nil
   irb(main):008:0> /i/.match(o)
   => #<MatchData:0x401eec60>

> The Regexp#match method could be implemented to take ANY object
> that implemented a some subset of the String API.

I think there's a semantic or perhaps definitional issue here, though.
What does it mean for a regular expression to "match" an arbitrary
object?  I don't think it's just a matter of what methods the object
has.  The object has to match the pattern, and the patterns are
descriptions of strings.  I'm not sure how you would detect a pattern
like /[A-Z]{3}(\d\d)?/ in something that wasn't a string.


David

-- 
David A. Black
dblack@wobblini.net