From: johnson.joel.b@...
Date: 2020-10-20T18:31:10+00:00
Subject: [ruby-core:100448] [Ruby master Misc#17199] id outputed by inspect and to_s output does not allow to find actual object_id and vice-versa

Issue #17199 has been updated by jorel (Joel Johnson).


Similarly, the `object_id` and object addresses are potentially problematic when making use of `ObjectSpace.trace_object_allocations_start` and dumping the json data periodically in trying to match up the object over time if `GC.compact` has happened. 

I think this highlights having `object_id` being a nice higher level concept for these use cases instead of relying on the address that is effectively an implementation detail.

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Misc #17199: id outputed by inspect and to_s output does not allow to find actual object_id and vice-versa
https://bugs.ruby-lang.org/issues/17199#change-88067

* Author: Annih (Baptiste Courtois)
* Status: Open
* Priority: Normal
----------------------------------------
Hello, here is my first ruby issue sorry in advance if it is incorrectly filled.

# Issue

The value returned by `#object_id` is not aligned anymore with displayed info in `#inspect` and `#to_s` methods.

## with ruby < 2.7

``` ruby
Object.new.tap { |o| p "#to_s=#{o.to_s}, #inspect=#{o.inspect}, #__id__=#{o.__id__}, shifted_id=#{(o.__id__ << 1).to_s(16)}" }
"#to_s=#<Object:0x0000000000d202a8>, #inspect=#<Object:0x0000000000d202a8>, #__id__=6881620, shifted_id=d202a8"
```

## with ruby >= 2.7

``` ruby
 Object.new.tap { |o| p "#to_s=#{o.to_s}, #inspect=#{o.inspect}, #__id__=#{o.__id__}, shifted_id=#{(o.__id__ << 1).to
s(16)}" }
"#to_s=#<Object:0x0000555dc8640b88>, #inspect=#<Object:0x0000555dc8640b88>, #__id__=220, shifted_id=1b8"
```


# Consequences

It makes harder:
- to implement a clean override of the `#inspect` method. i.e. How to keep the same output without ability to compute to the same "object_id" value.
- to debug the object using the inspect output. i.e. `ObjectSpace._id2ref(id_from_inspect >> 1)` used to work, now it doesn't (`RangeError: <xXx> is not id value`).

# Suggestion

IMHO either:
- the `#to_s` and `#inspect` documentation are obsolete `The default [...] [shows|prints] [...] an encoding of the object id` and the change could have been a bit more advertised
- they should use the result of `#object_id` instead of displaying the object pointer address

Another solution could be to provide a method to get access to the address, but I'm not sure you want that.

P.S. While debugging my problem I found [this ruby-forum thread](https://www.ruby-forum.com/t/understanding-object-id-in-ruby-2-7/260268/4) where people dived a bit more than me into ruby's code.



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