ruby - 是否可以从父类创建子类的实例？

Question

我尝试在 Ruby 中定义操作语义，仅用于学习目的。我想定义如下操作:加、乘、减、除。

代码如下:

class Operation < Struct.new(:left, :right)
  def inspect
    "#{self}"
  end

  def reducible?
    true
  end 
end

class Add < Operation
  def to_s
    "#{left} + #{right}"
  end

  def reduce
    if left.reducible?
      Add.new(left.reduce, right)
    elsif right.reducible?
      Add.new(left, right.reduce)
    else
      Number.new(left.value + right.value)
    end
  end

end

class Multiply < Operation
  def to_s
    "#{left} * #{right}"
  end

   def reduce
    if left.reducible?
      Multiply.new(left.reduce, right)
    elsif right.reducible?
      Multiply.new(left, right.reduce)
    else
      Number.new(left.value + right.value)
    end
  end
end

是否有可能拥有相同的东西，但在 Operation 类中定义 reduce，但在 Operation 中创建某个特定子类的实例类(class)？

提前致谢。

Answer 1

是的。

class Operation
  def reduce
    if left.reducible?
      self.class.new(left.reduce, right)
    elsif right.reducible?
      self.class.new(left, right.reduce)
    else
      Number.new(left.value + right.value)
    end
  end
end