Ruby-在超类中调用另一个Class方法

class A
  def self.a
    puts \"self: #{self}; superclass: #{superclass}\"
  end
end

class B < A
  class << self; undef_method(:a); end  # I\'m not allowed to use B.a
  def self.b
    # here I want to call A.a with B as self.
  end
end  

A.a  #=> self: A; superclass: Object
B.b  #=> self: B; superclass: A (expected)

alias_method

class B < A
  def self.b
    instance_eval(&A.method(:a).to_proc)
  end
end

ArgumentError

A.method(:a)

B

class B < A
  def self.b
    A.method(:a).unbind.bind(self).call
  end
end

class B < A
  class << self
    define_method :b, A.method(:a)
  end
end

B.a

class B < A
  def self.b
    a #=> self: B; superclass: A
  end
end