From: Robert Klemme <bob.news@...>
Date: 2004-11-10T17:33:31+09:00
Subject: Re: When is a key not a key?


"Dave Burt" <dave@burt.id.au> schrieb im Newsbeitrag
news:D7kkd.31098$K7.23161@news-server.bigpond.net.au...
> Hi,
>
> I hesitate to write because some of my code here is pretty evil, but
this
> problem is weirding me out a bit.
>
> I have a hash (loan_shark) indexed by instances of a particular struct
> (Player).
>
> The hash seems to be failing to find its keys when I try to look them
up.
> Like this:
>
> loan_shark.size  #=> 4
> loan_shark.has_key?(loan_shark.keys[0])  #=> false
>
> Any ideas?

Two possible reasons come to mind:

 - keys are modified after they were inserted into the hash but you did
not rehash

 - some of the instances that you put into the Player struct do not
implement #eql? and #hash appropriately.  Did you verify that newb.eql?(
newb ) is true?

Solutions to both could be to implement #eql? and #hash on your own, for
example if only "name" is the key.  From what I read I feel that :hands
does change over time and thus is maybe not suited to be included in the
key or the key's #hash and #eql? calculation.

Kind regards

    robert



>
> The background is something like this:
>
>  Player = Struct.new(:name, :bankroll, :hands)
> ...
>   loan_shark = {}
> ...
>       newb = Player.new("Fred", some_dollars)
> ...
>       loan_shark[newb] = some_dollars
> ...
>       players << newb
>
> If you feel the need, you can get all the code (about 15k) here:
> http://www.dave.burt.id.au/ruby/blackjack.rb
> http://www.dave.burt.id.au/ruby/cards.rb
> (The issue can be found near blackjack.rb:304, complete with futile
> debugging code)
>
> Cheers,
> Dave
>
>