可以从父类创建子类的实例吗？

Question

我尝试在Ruby中定义操作语义,仅用于学习目的.我想定义一些操作:add,multiply,subtraction,division.

这是代码:

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

是否有可能有相同的东西,但reduce在Operation类中定义,但在类中创建一些特定子类的实例Operation？

提前致谢.

Answer 1

是.

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