From: "Florian Groß" <florgro@...>
Date: 2005-05-05T21:54:10+09:00
Subject: Re: Whats so different about a Hash?

Andrew Walrond wrote:

> So if a.eql?(b), then a.hash MUST EQUAL b.hash.
> 
> Lets see:
> 
>  irb(main):038:0> a={1=>2}
>  => {1=>2}
>  irb(main):039:0> b={1=>2}
>  => {1=>2}
>  irb(main):040:0> a.eql?(b)
>  => true
>  irb(main):041:0> a.hash == b.hash
>  => false
> 
> So what gives?
> 
>  irb(main):034:0> {1=>2}.hash => -605137920
>  irb(main):035:0> {1=>2}.hash => -605147880
>  irb(main):036:0> {1=>2}.hash => -604944118

Odd, I thought Hash#hash had already been added to Ruby itself recently.

I guess you can workaround it like this:

class Hash
   def hash()
     [self.to_a, self.class].hash
   end
end

Though I am not sure if that is the correct semantics. (It could be the 
case that Hash#eql?() also compares default values.)