From: ts <decoux@...>
Date: 2001-03-30T20:32:01+09:00
Subject: [ruby-talk:13354] Re: Why is $_ local to the current scope?

>>>>> "J" == Jeremy Henty <jeremy@chaos.org.uk> writes:

J> In the chapter "The Ruby Language" of "Programming Ruby", $_ is the
J> only variable under the heading "Input/Output Variables" that has
J> local scope, so it seems a bit anomalous.

 $_ and $~ make reference to local variables.

 They are also thread local variables.

 If $_ was a global variable, it will be very difficult to use it.

 Just imagine 2 methods which work with $_. The first read a line, then
 call the second method (which modify $_). When the second method return
 you have lost the content of $_. This can give bug very difficult to
 find. 

 You have a similar problem, in a P language, when you forget 'local $_'
 in a sub and call another sub which modify $_.


J> Also, I'm surprised that 'ARGF.each do ...' sets $. but not $_.  Again
J> I don't see the reason for this.  Enlightenment will be welcomed!
 
 Well ruby-man say

  $_ :  The last input line of string by gets or readline.
                                         ^^^^    ^^^^^^^^
 $_ is set when you use the object as a file (sort of).

 When you use it as an iterator you can always write

  ARGF.each do |$_|
#   
  end



Guy Decoux