From: ts <decoux@...>
Date: 2005-11-22T02:27:31+09:00
Subject: Re: Statement modifiers causing confusion

>>>>> "D" == Dustin McCormick <djmccormick@gmail.com> writes:

D> while line = gets
 
 When ruby see the assignement `=' it will think that `line' is a variable.
 Then when it parse `gets' and because it's the first time than it seen it,
 it will resolved as a method call.

D>   puts line.downcase

 at this step, ruby now that `line' make reference to a variable

D> end

D> puts line.downcase while line = gets

 When it parse this line : it find `line' and this is the first time that
 it seen it and it's not an assignement. For ruby it's a method call

 When it parse 'line =', this time line will be referenced as a variable

 You can see it with something like this 

moulon% cat b.rb
#!/usr/bin/ruby
def line
   "ABC"
end

puts line.downcase while (line = gets).chomp != '123'
puts line
moulon% 

moulon% ./b.rb
XYZ
abc
ERT
abc
123
123
moulon% 

 The first reference is for the method #line, the 2 others for the variable
 `line' 

D> 02.07.rb:1: undefined local variable or method `line' for main:Object
D> (NameError)

 Here ruby is trying to say :

  1) at compile time, it has not found a variable line when it parsed this
     part of the source and it has resolved `line' as a method call

  2) at runtime, it has not found a method #line

D> line = 'This will never be seen...'
D> puts line.downcase while line = gets

 Here ruby has seen an affection before the while and it know that `line'
 make reference to a variable


Guy Decoux