gistfile1.rb

class A
  attr_accessor :id
  def initialize(_id)
    self.id = _id
  end

  def hash
    @id.hash
  end

  def eql?(other)
    @id.hash == other.hash
  end
  alias_method :==, :eql?
end

x = [A.new(1), A.new(2)]
y = [A.new(1), A.new(3)]

p (x&y)