class Foo
  attr_accessor :some_attr
  def initialize(val)
    self.some_attr = val
  end

  def ==(other)
    self.some_attr == other.some_attr
  end
end

x = Foo.new(1)
y = Foo.new(1)
z = Foo.new(2)

[x,y,z].uniq # => [x,y,z] :(

class Array
  def buniq(&block)
    uniq = {}
    each {|e| uniq[yield(e)] = e}
    uniq.values
  end
end

[x,y,z].buniq {|o| o.some_attr} #=> y,z