Re: [ ruby-Bugs-7253 ] Sets and String subclasses

On 12/13/06, murphy <[e-mail]> wrote:
> > I would expect the second puts to return 5, not nil.  In fact, I'd expect s.to_a[0] to return the same object as a.
> no problem with the subclass. the problem is here:
>
> require 'set'
> a = 'test'  # => "test"
> a.object_id  # => 931080
> Set[a].to_a.first.object_id  # => 931110
>
> why does Set duplicate its elements? Hash and Array don't do this.
> [murphy]

So the problem is here:

http://ruby-doc.org/core/classes/Hash.html#M002883
--------
hsh[key] = value => value
hsh.store(key, value) => value

Element Assignment輸ssociates the value given by value with the key
given by key. key should not have its value changed while it is in use
as a key (a String0 passed as a key will be duplicated and frozen).
--------

Set is implemented over Hash, using its .keys as the storage. (see
lib/1.8/set.rb)
Hash duplicates its keys to prevent the change.

if we add .freeze then it would return the same object:

require 'set'
a = 'test'.freeze  # => "test"
a.object_id  # => 931080
Set[a].to_a.first.object_id  # => 931080 or whatever it is