Re: [ ruby-Bugs-3506 ] Set containing duplicates

Joel VanderWerf wrote:
> Daniel Berger wrote:
>> [e-mail] wrote:
>>> Bugs item #3506, was opened at 2006-02-08 22:52
>>> You can respond by visiting:
>>> http://rubyforge.org/tracker/?func=detail&atid=1698&aid=3506&group_id=426
>>>
>>> Category: Core
>>> Group: None
>>> Status: Open
>>> Resolution: None
>>> Priority: 3
>>> Submitted By: Stefan Rusterholz (rstefan)
>>> Assigned to: Nobody (None)
>>> Summary: Set containing duplicates
>>>
>>> Initial Comment:
>>> If an object added to a set becomes modified and added again it will
>>> be in the set twice.
>>> A fix to this would be to add "@hash.rehash" in "def add(o)" and "def
>>> merge(enum)". Though this might minder the speed advantage of set.
>>> OTOH Set becomes quite useless if it is impossible to add without
>>> checking first if the element already contained.
>> I don't see it:
>>
>> require "set"
>>
>> x = "foo"
>>
>> set = Set[x,"bar","baz","foo"]
>> p set # #<Set: {"baz", "foo", "bar"}>
>>
>> set.add("foo")
>> p set # #<Set: {"baz", "foo", "bar"}>
>>
>> x.chomp!
>> set.add(x)
>> p set ##<Set: {"baz", "foo", "bar"}>
>>
>> Can anyone demonstrate the bug he is referring to?
>>
>> - Dan
> 
> irb(main):020:0> s = Set[]
> => #<Set: {}>
> irb(main):021:0> a = []
> => []
> irb(main):022:0> s << a
> => #<Set: {[]}>
> irb(main):023:0> a << 3
> => [3]
> irb(main):024:0> s << a
> => #<Set: {[3], [3]}>
> 

I don't think it's really a bug. If you have a set with members (like
Arrays) that hash based on their contents (rather than object id), and
if you modify those members, then you should rehash. It's the same
"problem" with Hash:

irb(main):025:0> h = {}
=> {}
irb(main):026:0> h[a] = 1
=> 1
irb(main):027:0> h
=> {[3]=>1}
irb(main):028:0> a << 4
=> [3, 4]
irb(main):029:0> h[a] = 2
=> 2
irb(main):030:0> h
=> {[3, 4]=>2, [3, 4]=>1}

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407