1

我需要加载一个 YAML 文件（我正在尝试使用 SettingsLogic），并且我希望实例加载与其同名的YAML。简要地：

class MySettings < SettingsLogic
  source "whatever_the_instance_is_called.yml"

# Do some other stuff here
end

basic_config = MySettings.new    # loads & parses basic_config.yml
advanced_cfg = MySettings.new    # loads & parses advanced_cfg.yml
...and so on...

原因是我还不知道我必须加载哪些配置文件，然后输入：

my_config = MySettings.new("my_config.yml")

或者

my_config = MySettings.new(:MyConfig)

只是似乎在重复自己。

我浏览了 Google 和 Stackoverflow，最接近答案的是“获取实例名称”或关于实例名称无意义的讨论！（但是，我可能弄错了查询。）

我试过了instance#class，而且instance#name；我也试过了 instance#_id2ref(self)。

我错过了什么？！

提前致谢！

4

4 回答 4

2

好的，所以对于局部变量赋值，存在一些障碍，例如该赋值可能比局部变量符号添加到局部变量列表稍晚一些。但这是我ConstMagicErsatz用来实现类似于开箱即用的 Ruby 常量魔法的模块：

a = Class.new
a.name #=> nil - anonymous
ABC = a # constant magic at work
a.name #=> "ABC"

这里的优点是您不必编写 ABC = Class.new( name: "ABC" )，name 被“神奇地”分配。这也适用于 Struct 类：

Koko = Struct.new
Koko.name #=> "Koko"

但没有其他课程。所以这里是我的ConstMagicErsatz，允许你做

class MySettings < SettingsLogic
  include ConstMagicErsatz
end

ABC = MySettings.new
ABC.name #=> "ABC"

也

a = MySettings.new name: "ABC"
a.name #=> "ABC"

它是这样的：

module ConstMagicErsatz
  def self.included receiver
    receiver.class_variable_set :@@instances, Hash.new
    receiver.class_variable_set :@@nameless_instances, Array.new
    receiver.extend ConstMagicClassMethods
  end

  # The receiver class will obtain #name pseudo getter method.
  def name
    self.class.const_magic
    name_string = self.class.instances[ self ].to_s
    name_string.nil? ? nil : name_string.demodulize
  end

  # The receiver class will obtain #name setter method
  def name= ɴ
    self.class.const_magic
    self.class.instances[ self ] = ɴ.to_s
  end

  module ConstMagicClassMethods
    # #new method will consume either:
    # 1. any parameter named :name or :ɴ from among the named parameters,
    # or,
    # 2. the first parameter from among the ordered parameters,
    # and invoke #new of the receiver class with the remaining arguments.
    def new( *args, &block )
      oo = args.extract_options!
      # consume :name named argument if it was supplied
      ɴς = if oo[:name] then oo.delete( :name ).to_s
           elsif oo[:ɴ] then oo.delete( :ɴ ).to_s
           else nil end
      # but do not consume the first ordered argument
      # and call #new method of the receiver class with the remaining args:
      instance = super *args, oo, &block
      # having obtained the instance, attach the name to it
      instances.merge!( instance => ɴς )
      return instance
    end

    # The method will search the namespace for constants to which the objects
    # of the receiver class, that are so far nameless, are assigned, and name
    # them by the first such constant found. The method returns the number of
    # remaining nameless instances.
    def const_magic
      self.nameless_instances = 
        class_variable_get( :@@instances ).select{ |key, val| val.null? }.keys
      return 0 if nameless_instances.size == 0
      catch :no_nameless_instances do search_namespace_and_subspaces Object end
      return nameless_instances.size
    end # def const_magic

    # @@instances getter and setter for the target class
    def instances; const_magic; class_variable_get :@@instances end
    def instances= val; class_variable_set :@@instances, val end

    # @@nameless_instances getter for the target class
    def nameless_instances; class_variable_get :@@nameless_instances end
    def nameless_instances= val; class_variable_set :@@nameless_instances, val end

    private

    # Checks all the constants in some module's namespace, recursivy
    def search_namespace_and_subspaces( ɱodule, occupied = [] )
      occupied << ɱodule.object_id           # mark the module "occupied"

      # Get all the constants of ɱodule namespace (in reverse - more effic.)
      const_symbols = ɱodule.constants( false ).reverse

      # check contents of these constant for wanted objects
      const_symbols.each do |sym|
        # puts "#{ɱodule}::#{sym}" # DEBUG
        # get the constant contents
        obj = ɱodule.const_get( sym ) rescue nil
        # is it a wanted object?
        if nameless_instances.map( &:object_id ).include? obj.object_id then
          class_variable_get( :@@instances )[ obj ] = ɱodule.name + "::#{sym}"
          nameless_instances.delete obj
          # and stop working in case there are no more unnamed instances
          throw :no_nameless_instances if nameless_instances.empty?
        end
      end

      # and recursively descend into the subspaces
      const_symbols.each do |sym|
        obj = ɱodule.const_get sym rescue nil # get the const value
        search_namespace_and_subspaces( obj, occupied ) unless
          occupied.include? obj.object_id if obj.kind_of? Module
      end
    end
  end # module ConstMagicClassMethods
end # module ConstMagicErsatz

上面的代码实现了对整个 Ruby 命名空间的自动搜索，目的是在调用 #name 方法时找出哪个常量引用给定的实例。

使用常量的唯一限制是你必须将它大写。当然，您想要的是在对象已经生成并分配给常量之后修改它的元类。再一次，因为没有钩子，你必须找到这样做的机会，比如当新对象第一次被用于它的目的时。所以，有

ABC = MySettings.new

然后，当第一次使用 MySettings 实例时，在做任何其他事情之前，修补它的元类：

class MySettings
  def do_something_useful
    # before doing it
    instance_name = self.name
    singleton_class.class_exec { source "#{instance_name}.yml" }
  end

  # do other useful things
end
于 2012-11-09T00:48:20.477 回答
0

好吧，如果你有大量的变量要实例化，我个人只是创建一个Hash来保存它们，这样更干净。现在要实例化所有这些，您可以对所有 yaml 文件进行循环：

my_settings = {}
[:basic_config, :advanced_cfg, :some_yaml, :some_yaml2].each do |yaml_to_parse|
  my_settings[yaml_to_parse] = MySettings.new(yaml_to_parse)
end

确保你的initialize方法MySettings处理你给它的符号！

然后像这样得到你的变量：

my_settings[:advanced_cfg]
于 2012-11-08T23:57:07.823 回答
0

不幸的是，Ruby 没有用于变量赋值的钩子，但这可以解决。策略大纲如下：首先，您需要让您的MySettings.new方法来评估调用者绑定中的代码。local_variables然后，您将通过调用那里的方法找到调用者绑定中的局部变量符号列表。之后，您将遍历它们以查找哪个引用了您的自定义方法super中调用返回的实例。MySettings.new你会将它的符号传递给source方法调用。

于 2012-11-09T00:12:48.983 回答
0

你不应该也可以吗

File.open(File.join(File.expand_path(File.dir_name(__FILE__)), foo.class), "r")

或者

require foo.class

第一个不一定要那么复杂。但是，如果我对您的理解正确，您可以直接在 require 或 file load 语句中使用 foo.class 。

根据需要调整 YAML 加载，但 #class 返回一个普通的旧字符串。

于 2012-11-08T23:51:41.390 回答