From: Dan Doel <djd15@...>
Date: 2004-01-28T19:14:08+09:00
Subject: Re: newbee question about "missing" hash methods +, += and <<

benny wrote:

>I wasn't successful in deleting a key from hash, which is an hash on its own.
>
>h = { {"foo"=>"bar"} =>1 }.delete({"foo"=>"bar"})
>
>doesn't seem to work. any idea?
>
>if there is no way to delete such a key then there would be no difference to "-" : 
>in both cases the whole entry would be deleted. 
>
>{"foo" => "bar"}.delete("foo") = {"foo" => "bar"} - {"foo" => "bar"} 
>
>anyway its a very special case to have a key which is a hash, I think. I don't see where such a
>thing would make sense and was suprised that its possible (maybe ruby is the only
>language to allow such a thing?).
>
>when I think of a "key" I think of a quick index-like reference to find something quickly. 
>  
>
[dolio 04:59:10 ~]$ cat prac.rb
#!/usr/bin/ruby

a = { 1 => 2 }
b = { a => 3 }

p b

b.delete a

p b

[dolio 04:59:14 ~]$ ./prac.rb
{{1=>2}=>3}
{}

In your test, the { "foo" => "bar" } stored in the first hash wasn't the 
same as the
one you tried to delete later (different objects/ids, same structure). 
Hashes for
objects only have to be the same if #eql? returns true between them, and 
that's
not necessarily the case for two structrurally identical hashes (it's 
true only if they're
the same object).

As I recall, in Python you can only use immutable things as keys to hashes.
However, in Java, for example, you can use any Object, whether it's a 
String or
a Hashtable, so Ruby isn't alone.

- Dan