当前对象/类实例的名称

Question

我需要加载一个YAML文件(我正在试验SettingsLogic)，并且我希望实例以与它相同的名称加载YAML。简要说明：

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...

原因是我还不知道必须加载哪些配置文件，并输入：

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

或

my_config = MySettings.new(:MyConfig) 

好像是在重复我自己。

我环顾了一下Google和Stackoverflow，最近找到的答案要么是"Get Instance Name“，要么是关于实例名有多无意义的讨论！(不过，我可能把查询搞错了。)

我试过instance#class和instance#name，也试过instance#_id2ref(self)。

我遗漏了什么？!

提前感谢！

Answer 1

好的，因此对于局部变量赋值，存在一些障碍，例如，分配可能比局部变量列表中添加的局部变量符号稍晚一些。但是下面是我的模块ConstMagicErsatz，我用它来实现类似于开箱即用的Ruby常量魔法：

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(名称："ABC“)，名称被指定为‘魔术’。这也适用于Struct类：

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

但没有其他课程。所以我的ConstMagicErsatz允许你做

class MySettings < SettingsLogic
  include ConstMagicErsatz
end

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

以及

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

下面是：

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

上面的代码实现了整个Ruby命名空间的自动搜索，目的是在调用#name方法时找到引用给定实例的常量。

唯一使用常量的约束是，您必须将其大写。当然，您想要的是在对象已经生成并分配给常量之后修改对象的元类。同样，由于没有钩子，所以您必须找到这样做的时机，例如新对象最初用于其目的的时间。所以，有

ABC = MySettings.new

然后，当第一次使用MySettings实例时，在执行任何其他操作之前，修补其元类：

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

Answer 2

你不应该这样做吗？

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

或

require foo.class

第一个问题不一定那么复杂。但是，如果我对您的理解是正确的，您可以直接在require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。

Answer 3

如果你有大量的变量要实例化，我会亲自创建一个Hash来保存它们，这样就更干净了。现在，要实例化所有这些，您可以执行一个循环(其他所有yaml文件)：

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

确保您的initialize方法在MySettings中处理您给它的符号！

然后得到这样的变量：

my_settings[:advanced_cfg]