Ruby的数组如何.|比较要素是否相等？

class Obj
  attr :c,true

  def == that
    p '=='
    that.c == self.c
  end
  def <=> that
    p '<=>'
    that.c <=> self.c
  end
  def equal? that
    p 'equal?'
    that.c.equal? self.c
  end
  def eql? that
    p 'eql?'
    that.c.eql? self.c
  end
end

a = Obj.new
b = Obj.new

a.c = 1
b.c = 1

p [a] | [b]

它打印2个对象,但它应该打印1个对象.没有调用任何比较方法. Array怎么样.|比较平等？