Difference between == and case?

Question

I'm new to Ruby and am trying to work something out which is confusing me. While writing a simple parser, I found that comparing a char with a == would produce a different result than comparing it with a case expression:

File.open('Quote.txt') do |f|
  f.chars.each do |c|
    puts c == '"' ? 'Quote' : 'Err'

    puts case c
    when '"' then 'QuoteCase'
    else          'ErrCase'
    end

    p c == '"', c === '"', c
  end
end

Assuming Quote.txt is a 1-byte file containing a single quote character (0x22), this produces:

Quote
ErrCase
true
true
"\""

I'm assuming I've done something wrong, but I can't figure out what it is. Can anyone help?

This is in Ruby 1.9.2, by the way.

Answer 1

case uses the triple-equal === operator to check each case.

That said, I don't know why your example isn't working:

> c = "\""
> c == "\""
=> true
> c === "\""
=> true

Try removing the .each and explicitly setting c to the quote character and see what happens.

Generally, === is more forgiving than == in Ruby, so I can't imagine a case where == would match and === wouldn't.

Edit: I've just copied your code, with the same input (a file with a single " character) and got the following output:

Quote
QuoteCase
Err
ErrCase

(the last two are from the newline at the end of the file that Vim insists on).

Answer 2

It looks like a bug in YARV on windows. I get the correct output in JRuby 1.6.0:

# ruby -v
ruby 1.9.2p180 (2011-02-18) [i386-mingw32]

# ruby test.rb
Quote
ErrCase
true
true
"\""

# jruby --1.9 -v
jruby 1.6.0 (ruby 1.9.2 patchlevel 136) (2011-03-15 f3b6154) (Java HotSpot(TM) Client VM 1.7.0-ea) [Windows XP-x86-java]

# jruby --1.9 test.rb
Quote
QuoteCase
true
true
"\""