From: Stefan Kruger <stefan.kruger@...>
Date: 2007-06-15T03:01:23+09:00
Subject: Characters and strings oddness

Hi there Rubyists -

I'm trying to learn the language, coming from a long background in Perl.

Here's what I want to do: pick out a double-quoted string inside
another string,
respecting embedded, backslashed quotes:

line = ' a string "properly \"quoted\" that ends" here '
quoted = '"properly \"quoted\" that ends"'

If Ruby had the same regexes as Perl, I'd say something like

line.gsub!(/^\s*(\".*?(?<!\\)\")\s*/, '')

and have my quoted string pop out in $1. In fact, TextMate groks that
regex, too.
Ruby don't like the negative look-behind, unfortunately.

Ok, let's do a loop then. I finally arrived at:

string = "\""
if line.gsub!(/^.*?(\")/, '')
  (0..line.length).each do |i|
    string << line[i]
    break if i>0 && (line[i, 1] == "\"") && (line[i-1, 1] != '\\')
  end
end

which works. However.. I'm puzzled by Ruby's way of handling strings. A string
is - essentially - a set of bytes, not unlike a char[] in C. Is there
really no way
of defining character literals in Ruby? I was surprised to find that I
couldn't say

Stefan-Krugers-Computer:~ stefan$ irb
irb(main):001:0> string = 'this is a string'
=> "this is a string"
irb(main):002:0> string[0] == 't'
=> false

whereas i *can* say

irb(main):003:0> string[0, 1] == 't'
=> true

Now, in my little loop experiment above I tried the following:

delim = "\""
string = delim
if line.gsub!(/^.*?(\")/, '')
  (0..line.length).each do |i|
    string << line[i]
    break if i>0 && (line[i, 1] == delim) && (line[i-1, 1] != '\\')
  end
end

TypeError: can't convert nil into String

method <<    in test.rb at line 9
at top level    in test.rb at line 9
at top level    in test.rb at line 8

I'm at a loss to understand why that gives an error.

-- 
Stefan Kruger <stefan.kruger@gmail.com>