模拟默认对象#检查输出？

Question

o = Object.new
o.instance_eval { @str = "foo" }
p o # => #<Object:0x5dd1a0 @foo="bar">

这很好.p使用对象作为参数调用将打印对象inspect方法的输出.但是,不幸的是,如果对象有一个to_s方法被覆盖,那么它将输出该输出:

class << o
  def to_s; @str; end
end
p o.to_s # => "foo"
p o # => foo

所以要解决这个问题,我们必须inspect在对象上定义一个方法:

class << o
  def inspect; "blah"; end
end
p o # => "blah"

如何使我的对象的inspect方法输出默认的Ruby方式,如我的第一个代码示例的第3行所示？

我最接近的是下面的,但我不确定它是否正确

class << o
  def inspect
    vars = instance_variables.collect { |v| v.to_s << "=#{instance_variable_get(v).inspect}"}.join(", ")
    "#<#{self.class}:0x#{object_id} #{vars}>"
  end
end

Answer 1

要使数字与原始实现匹配,您只需要将object_id向左移动一位,如下所示:

(object_id << 1).to_s(16)

必须有一个额外的位用于标志.

Answer 2

默认inspect方法结果非常复杂,因为它需要正确处理对自身的递归调用.这是一个基于Rubinius源代码的实现,它忽略了存在to_s.

module DefaultInspect

    Thread.current[:inspected_objects] = {}

    def inspected_objects
      Thread.current[:inspected_objects]
    end

    def inspect_recursion_guard
      inspected_objects[object_id] = true
      begin
        yield
      ensure
        inspected_objects.delete object_id
      end
    end

    def inspect_recursion?
      inspected_objects[object_id]    
    end

    def inspect
      prefix = "#<#{self.class}:0x#{self.__id__.to_s(16)}"

      # If it's already been inspected, return the ...
      return "#{prefix} ...>" if inspect_recursion?

      # Otherwise, gather the ivars and show them.
      parts = []

      inspect_recursion_guard do
        instance_variables.each do |var|
          parts << "#{var}=#{instance_variable_get(var).inspect}"
        end
      end

      if parts.empty?
        str = "#{prefix}>"
      else
        str = "#{prefix} #{parts.join(' ')}>"
      end

      str.taint if tainted?

      return str
    end

end

要使用此模块,您可以执行以下操作:

class Foo

  include DefaultInspect

  def to_s
    @foo
  end
end

f = Foo.new
f.instance_eval { @foo = f }
p f     #=> #<Foo:0x8042ad58 @foo=#<Foo:0x8042ad58 ...>>