Question

我需要加载一个YAML文件（我正在尝试使用SettingsLogic），我希望该实例使用与它相同的名称加载YAML。简言之：

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...

原因我还不知道我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)

似乎在重复自己。

我浏览了Google和Stackoverflow，我最接近答案的是“Get Instance Name”或关于实例名称无意义的讨论！（但我可能会错误地查询错误。）

我尝试了instance#class和instance#name;我也试过了instance#_id2ref(self)。

我缺少什么？！

提前致谢！

Answer 1

O.K。，因此对于局部变量赋值，存在障碍，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发生。但这是我的模块ConstMagicErsatz，我曾经用它来实现类似于开箱即用的Ruby常量魔术：

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“魔术”分配。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允许你这样做

class MySettings < SettingsLogic
  include ConstMagicErsatz
end

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

以及

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

这就是：

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

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

使用常量的唯一约束是，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后修改对象的元类。既然没有钩子，你必须找到这样做的机会，例如当新对象首次用于其目的时。所以，有

ABC = MySettings.new

然后，当您第一次使用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

你不应该做任何一件事

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

或

require foo.class

第一个不一定必须那么复杂。但如果我正确理解你，你可以直接在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。

Answer 3

不幸的是，Ruby没有用于变量赋值的钩子，但是这可以解决。战略大纲如下：首先，您需要将MySettings.new方法转到eval code in the caller's binding。然后，您将通过在那里调用local_variables方法找到调用者绑定中的局部变量符号列表。然后，您将迭代它们以查找哪个引用了super方法中MySettings.new调用返回的实例。并且您将其符号传递给source方法调用。

当前对象/类实例的名称

3 个答案: