如何计算ruby中的类的现有实例？ [英] How to count existing instances of a class in ruby?

问题描述

以下是来自这个问题的想法：在创建对象时，增加一个类变量。当对象被收集时，将其递减。正如你所看到的，调用finalizer，并且 @@ no_foo 得到递减。但是当我稍后查询它时，减量就消失了。似乎价值只会上涨，永远不会下跌（如果我创建两个对象，它会显示2）。我错过了一些明显的东西？

Here's an idea from this question: Upon object creation, increment a class variable. When object gets collected, decrement it. As you can observe, finalizer is called, and @@no_foo gets decremented. But when I query it a moment later, decrement is gone. Seems that value is going only up, never down (if I create two objects, it will show 2). Am I missing something obvious?

class Foo
  @@no_foo = 0

  def initialize
    puts 'creating object'
    @@no_foo += 1
    ObjectSpace.define_finalizer(self, proc { self.delete })
  end

  def delete
    puts 'deleting object'
    @@no_foo # => 1
    @@no_foo -= 1
    @@no_foo # => 0
  end

  def self.no_foo
    @@no_foo # => 0, 1
  end
end

Foo.no_foo # => 0
f = Foo.new
f = nil

GC.start
Foo.no_foo # => 1

# >> creating object
# >> deleting object

推荐答案

它可以工作，但有循环引用定稿。您的终结器取决于应该收集的对象的绑定。请参阅此解决方案。

It can work, but there's circular reference in finalization. Your finalizer depends on the binding of an object that should be collected. See this solution.

class Foo
  @@no_foo = 0

  def initialize
    @@no_foo += 1
    ObjectSpace.define_finalizer(self, Foo.method(:delete))
  end

  def self.delete id # also this argument seems to be necessary
    @@no_foo -= 1
  end

  def self.no_foo
    @@no_foo
  end
end

Foo.no_foo # => 0
1000.times{Foo.new}
Foo.no_foo # => 1000

GC.start
Foo.no_foo # => 0

这篇关于如何计算ruby中的类的现有实例？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！