From: Florian Gilcher <flo@...>
Date: 2010-03-01T23:21:57+09:00
Subject: Re: What is '?' in Ruby?


On Mar 1, 2010, at 1:31 PM, Alexander Bubnov wrote:

> Hello!
> To clarify the question I need to say some more.
> I know
> Ruby 1.8 '?a' => 97
> Ruby 1.9 '?a' => "a"
> Really I would like to where I can get specification of operator,
> keyword, function or something else I do know what is name of '?'...
> I have surfed ruby-lang.org and ruby-doc.org but can't find information
> about it. Is it an unofficial something?
> Just a bit here http://www.ruby-doc.org/docs/ProgrammingRuby/, "Standard
> Types" chapter:
> ?a                        # character code
> 
> But it is related to 1.8 version, not for 1.9.
> Please just point to chapter of ruby specification where I can find
> anything about '?' if it is. And are there methods which helps to know
> what is '?'?

Ruby 1.8 sees strings as a sequence of bytes. So

  "a"[0] #=> 97

yields 97 (because 97 is the value representing the character a in an ASCII-String). If you want to compare this to some character, you need the character code of "a" (because no one wants to have an ASCII-Table next to them when programming). ?a gives you the character code of a. So
 
  "a"[0] == ?a #=> true
  "a"[0] == "a" #=> false

Now, things have changed in the String world in Ruby 1.9. Strings now know their encoding and return charactes instead of codepoints when accessing single characters.

  "a"[0] #=> "a"

To make sure that legacy applications do not break, ?a will now return "a", so now the behaviour is as follows:

  "a"[0] == ?a #=> true
  "a"[0] == "a" #=> true

Regards,
Florian Gilcher