[ruby-core:17625] Can't have more than 2*21 unique symbols?

Hi,

I found some interesting blog post with bug report against MRI, and it
seems  that it relates to a number of symbols MRI can handle.

The original report is here:
http://ninh.nl/blog/2008/07/06/ruby-bug/

Here's a very simple example:
obj = Object.new
(1..20_000_000).each { |i|
  puts "Object responds to #{i}" if obj.respond_to?(i.to_s)
}

Try to run it on *any* MRI version and you'll see:
Object responds to 2094132
Object responds to 2094133
Object responds to 2094134
Object responds to 2094141
Object responds to 2094144
Object responds to 2094156
Object responds to 2094158
Object responds to 2094159
Object responds to 2094160
Object responds to 2094249
Object responds to 4191284
Object responds to 4191285
Object responds to 4191286
....

And the object *DOES* respond to those :)

For example, :"2094132" is actually :nil?, etc.

If you take a look at the series above, you'll see that they repeat
every 2**21th iteration.

So, effectively, MRI can handle at most 2**21 unique symbols and then
it silently overflows thus producing non-unique symbols.

I've checked with JRuby, and it can handle more than 2*21 symbols.

Thanks,
  --Vladimir