从单例类中检索Ruby对象? [英] Retrieve a Ruby object from its singleton class?

问题描述

可以从Ruby访问单个类对象:

It is possible to access a singleton class from a Ruby object with:

some_object.singleton_class

是否可以执行相反的操作:在单例类内部时访问原始对象?

Is it possible to do the reverse operation : access the original object when inside the singleton class?

class << some_object
  # how to reference some_object without actually typing some_object?
end

我想干燥此方法:

class Example
  PARENTS = []
  class << PARENTS
    FATHER = :father
    MOTHER = :mother
    PARENTS.push(FATHER, MOTHER)
  end
end

，并尝试用更通用的内容替换类中的PARENTS.

and tried to replace PARENTS inside the class with something more generic.

推荐答案

我不知道任何内置方法或关键字，但是您可以编写一个将(singleton)方法添加到对象的singleton类的方法，返回对象本身:

I'm not aware of any built-in method or keyword but you could write a method that adds a (singleton) method to an object's singleton class, returning the object itself:

class Object
  def define_instance_accessor(method_name = :instance)
    singleton_class.define_singleton_method(method_name, &method(:itself))
  end
end

用法:

obj = Object.new              #=> #<Object:0x00007ff58e8742f0>
obj.define_instance_accessor
obj.singleton_class.instance  #=> #<Object:0x00007ff58e8742f0>

在您的代码中:

class Example
  PARENTS = []
  PARENTS.define_instance_accessor
  class << PARENTS
    FATHER = :father
    MOTHER = :mother
    instance.push(FATHER, MOTHER)
  end
end

---

在内部，YARV将对象存储在名为__attached__的实例变量中.实例变量没有通常的@前缀，因此在Ruby中是不可见或不可访问的.

---

Internally, YARV stores the object in an instance variable called __attached__. The instance variable doesn't have the usual @ prefix, so it isn't visible or accessible from within Ruby.

这里有一个C扩展来公开它:

Here's a little C extension to expose it:

#include <ruby.h>

static VALUE
instance_accessor(VALUE klass)
{
    return rb_ivar_get(klass, rb_intern("__attached__"));
}

void Init_instance_accessor()
{
    rb_define_method(rb_cClass, "instance", instance_accessor, 0);
}

用法:

irb -r ./instance_accessor
> obj = Object.new
#=> #<Object:0x00007f94a11e1260>
> obj.singleton_class.instance
#=> #<Object:0x00007f94a11e1260>
>

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