Object#to_s vs id aka object_id

Question

I probably should take a course on using google, but I just can’t find out an answer.

When one calls to_s on the instance of class, that does not have an ancestor, overriding to_s, Object#to_s is being called and the output looks like:

"#<TestClass:0x136e3544>"

According to the documentation:

The default to_s prints the object’s class and an encoding of the object id.

What the heck means “encoded” here? It’s not an id itself:

▶ t = TestClass.new.to_s
#⇒ "#<TestClass:0x137e6b94>"
▶ t.__id__
#⇒ 163526070
▶ "0x%08x" % t.__id__
#⇒ "0x09bf35b6"

According to ruby source, it is a heap memory address:

str = rb_sprintf("#<%"PRIsVALUE":%p>", cname, (void*)obj);

Now the question is: is there any relation between __id__ and what’s being printed in default to_s at all?

NB Credits to @MarekLipka: possibly this behavior may be reproduced under VirtualBox only. It sounds like on native env the following does the trick:

"0x%08x" % (t.__id__ << 1)

It wasn't easy, but I found the answer to your question on SO. — Marek Lipka, May 22 '15 at 11:40
Thanks, @MarekLipka, but unfortunately the answer given there is either obsolete, or just not correct. For the class above: `"0x%08x" % (t.__id__ << 1) #⇒ "0x137e6b6c"`. The difference in last two digits is significant for me, since I want to keep compatibility with what ruby does. — Aleksei Matiushkin, May 22 '15 at 11:44
It's strange since I even tested it on my machine, 2.1.5 version and it was correct: `t = TestClass.new` `# => #` `'%x' % (t.object_id << 1)` `# => "2b798a8"` — Marek Lipka, May 22 '15 at 11:45
@MarekLipka Uhm. Please note, that `to_s` returned `0x137e6b94` (last two digits.) — Aleksei Matiushkin, May 22 '15 at 11:47
I tested it on 2.2.0 moment ago, same (correct) result. Strange. But I'm reopening the question, maybe someone has an idea why this happens in your environment. — Marek Lipka, May 22 '15 at 11:54
@MarekLipka I would blame VirtualBox I was testing under. On clean env everything is as expected. I updated the answer, please mark it back as a duplicate. — Aleksei Matiushkin, May 22 '15 at 11:57

Object#to_s vs __id__ aka object_id

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Object#to_s vs id aka object_id