Question

鉴于下面的Java代码，你可以在Ruby类中代表这两个static final变量的最接近的代码是什么？并且，在Ruby中是否可以区分private static和public static变量，就像在Java中一样？

public class DeviceController
{
  ...
  private static final Device myPrivateDevice = Device.getDevice("mydevice");
  public static final Device myPublicDevice = Device.getDevice("mydevice");
  ...
  public static void main(String args[])
  {
   ...
  }
}

Answer 1

我能想到的最终变量是将变量作为模块的实例变量：

class Device
    # Some static method to obtain the device
    def self.get_device(dev_name)
        # Need to return something that is always the same for the same argument
        dev_name
    end
end

module FinalDevice
    def get_device
        # Store the device as an instance variable of this module...
        # The instance variable is not directly available to a class that
        # includes this module.
        @fin ||= Device.get_device(:my_device).freeze
    end
end

class Foo
    include FinalDevice
    def initialize
        # Creating an instance variable here to demonstrate that an
        # instance of Foo cannot see the instance variable in FinalDevice,
        # but it can still see its own instance variables (of course).
        @my_instance_var = 1
    end
end

p Foo.new

p (Foo.new.get_device == Foo.new.get_device)

输出：

#<Foo:0xb78a74f8 @my_instance_var=1>
true

这里的技巧是通过将设备封装到模块中，您只能通过该模块访问设备。从类Foo开始，无法直接修改您正在访问的设备，而无需直接对Device类或FinalDevice模块执行操作。 freeze FinalDevice中的Foo电话可能适合或不适合，具体取决于您的需求。

如果您想制作公共和私人访问者，可以像这样修改class Foo include FinalDevice def initialize @my_instance_var = 1 end def get_device_public get_device end private def get_device_private get_device end private :get_device end：

FinalDevice::get_device

在这种情况下，您可能还需要修改@fin以获取参数。

更新：@banister指出FinalDevice中声明的Foo确实可以由Foo#inspect的实例访问。我懒得假设，因为它不在Foo的默认文本输出中，所以它不在@fin内。

您可以通过更明确地使FinalDevice成为class Device def self.get_device(dev_name) dev_name end end module FinalDevice def get_device FinalDevice::_get_device end protected def self._get_device @fin ||= Device.get_device(:my_device).freeze end end class Foo include FinalDevice def get_device_public get_device end def change_fin @fin = 6 @@fin = 8 end private def get_device_private get_device end private :get_device end f = Foo.new x = f.get_device_public f.change_fin puts("fin was #{x}, now it is #{f.get_device_public}")模块的实例变量来解决此问题：

fin was my_device, now it is my_device

哪个正确输出：

{{1}}

Answer 2

class DeviceController
  MY_DEVICE = Device.get_device("mydevice")
end

是的，require 'device'如果需要的话。

虽然没有什么可以阻止你在其他地方重新定义常量，除了警告：）

Answer 3

Ruby中的私有静态：

class DeviceController
    @@my_device = Device.get_device("mydevice")
end

Ruby中的public static：

class DeviceController       
    def self.my_device; @@my_device; end

    @@my_device = Device.get_device("mydevice")
end

Ruby没有'final'：）

Java中“private static final”和“public static final”类变量的最近Ruby表示？

4 个答案: