From: Mathieu Bouchard <matju@...>
Date: 2000-06-12T11:22:46-04:00
Subject: [ruby-talk:03339] Re: BUG or something?

> |Question, how does Hash computes the hash value of a String? or of any
> |object?
> By invoking `hash' method of key object.

well, not exactly. ts said:

> See the method hash
> Apparently ruby call the method hash for each object, except for T_FIXNUM
> (it return the value) and T_STRING (rb_str_hash)
> In 1.5 rb_str_hash is different than 1.4 (see #ifdef)

well, I've taken a look, and it seems that there is a performance hack: 
"hash" is called directly on a String, just like "ts" said. If it wasn't a
special case, then the following program would work. (that is, unless my
program has bugs)

--------8<----------------cut-here----------------8<--------istring.rb

class IString < String
	def == (other); upcase == other.upcase; end
	def eql? (other); upcase.eql?(other.upcase); end
	def hash; upcase.hash; end
end

print "$a = ";p $a = "foo"
print "$b = ";p $b = $a.upcase
print "$c = ";p $c = IString.new($a)

print "$c == $a : ";p $c == $a
print "$a == $c : ";p $a == $c
print "$c == $b : ";p $c == $b
print "$b == $c : ";p $b == $c

print "$a.hash == ";p $a.hash
print "$b.hash == ";p $b.hash
print "$c.hash == ";p $c.hash

$H = {}
$H[IString.new("unf")]=1;
$H[IString.new("UNF")]=2;
$H[IString.new("DOH")]=3;
$H[IString.new("doh")]=4;

p $H

--------8<----------------cut-here----------------8<--------end

btw, my error for not seeing the documentation for "hash". 
I was looking in String but it's documented in "Object". :-)



Mathieu Bouchard