《大话设计模式》ruby版代码：简单工厂模式

# -*- encoding: utf-8 -*-

#运算类
class Operation
    attr_accessor :number_a,:number_b
    
    def initialize(number_a = nil, number_b = nil)
        @number_a = number_a
        @number_b = number_b
    end
    
    def result
        0
    end
end

#加法类
class OperationAdd < Operation
    def result
        number_a + number_b
    end
end

#减法类
class OperationSub < Operation
    def result
        number_a - number_b
    end
end

#乘法类
class OperationMul < Operation
    def result
        number_a * number_b
    end
end

#除法类
class OperationDiv < Operation
    def result
        raise ‘除数不能为0‘ if number_b == 0    
        number_a / number_b
    end
end

#工厂类
class OperationFactory
    def self.create_operate(operate)
        case operate
        when ‘+‘
            OperationAdd.new()
        when ‘-‘
            OperationSub.new()
        when ‘*‘
            OperationMul.new()
        when ‘/‘
            OperationDiv.new()
        end
    end
end

oper = OperationFactory.create_operate(‘/‘)
oper.number_a = 1
oper.number_b = 2
p oper.result