From: Sebastian Hungerecker <sepp2k@...>
Date: 2008-09-14T20:29:37+09:00
Subject: Re: getting an array of unique objects of a class i wrote

Adam Akhtar wrote:
> class thing
> attr_accessor :name :job
> end

Thing = Struct.new(:name, :job)


> and i want to ensure that if i have an array of these objects there will
> be no duplicates. A duplicate would be where both the name and job are
> the same in both objects.
>
> I tried using uniq! but it didnt work. Not sure why (can someone explain
> that).

For uniq to work your class has to implement hash and eql?, so that for any 
two objects that you consider equal o1.hash == o2.hash and o1.eql?(o2) and 
for any two objects that you do not consider equal !o1.eql?(o2) (o1.hash may 
still be equal to o2.hash, but should not be).


> Ive heard of set, could that be used in this case to prevent duplicates
> being added?

If uniq does not work, set does not work either. Once you implement hash and 
eql?, yes, set can be used.
If you use Struct to define your class, like I demonstrated above hash and 
eql? will be defined automatically. If you can't use a struct, you could 
define them as such:
class Thing
  attr_accessor :name, :job
  def hash
    [name, job].hash
  end

  def eql?(other)
    [name, job].eql?([other.name, other.job])
  end
end


HTH,
Sebastian
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