From: Intransition <transfire@...>
Date: 2010-04-24T23:09:49+09:00
Subject: Re: #object_hexid



On Apr 24, 9:31 am, Brian Candler <b.cand...@pobox.com> wrote:
> Thomas Sawyer wrote:
> > Can anyone write a reliable Kernel#object_hexid, a method that returns
> > an object's id but in hex, just like Ruby's normal #inspect provides.
>
> > My attempts seems to break depending on the version of Ruby used.
>
> Can you show the failing examples? Is the portability problem between
> ruby 1.8.x and 1.9.x, or are you trying to make portable with JRuby,
> Rubinius, MacRuby etc?

That would be nice.

I recently got an error report from someone using 1.8.6:

  1) Failure: test_object_hexid(TCKernel) [./test/core/kernel/
test_object_hexid.rb:8]:
  <"#<Object:0x1a14ff4>"> expected but was
  <"#<Object:0xa14ff4>">.

I know what's causing this in my current implementation, but I've been
down this road before -- I tweak the implementation to satisfy one
error report and another seems to crop up. So I was hoping someone
might have a definitive answer.

> Is it important that object_hexid returns the same value as reported by
> #inspect, or just some unique id?

Yes.

> The obvious would be something like:
>
> >> module Kernel
> >> def object_hexid(o)
> >> o.object_id.to_s(16)
> >> end
> >> end
> => nil
> >> object_hexid("")
>
> => "3faf23593bf4"
>
> but I've not tested that on any more than MRI 1.8.7, and the hex ID is
> not the same as #inspect:
>
> >> class Foo; end
> => nil
> >> f = Foo.new
>
> => #<Foo:0x7f5e46b1c168>>> object_hexid(f)
>
> => "3faf2358e0b4"

Right. You have to shift the value one unit like Dominik's version.

At this point I think I am just going to go with the simple solution:

  "0x" << (__id__ << 1).to_s(16)

Previous error reports seem to be 1.8.6 related, and at this point I
think I will only support 1.8.7+. Hopefully the above definition is
consistent for all implementations. I think it would be nice if this
method was already provided -- I find it helpful in cases where I
write a custom #inspect method, but still wish to imitate Ruby's usual
format.