[ruby-core:81697] [Ruby trunk Bug#13498][Assigned] Weakref, Weakmap and define_finalizer don't work on frozen objects

[nobu@ruby-lang.org]

Issue #13498 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Assigned
Assignee set to nobu (Nobuyoshi Nakada)

Weakref is implemented by finalizer to notify that an object is collected, and you can't define finalizers on frozen objects.
Probably we need to move finalizer flags to a separate region (like bitmap marking).

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Bug #13498: Weakref, Weakmap and define_finalizer don't work on frozen objects
https://bugs.ruby-lang.org/issues/13498#change-65385

* Author: herwin (Herwin W)
* Status: Assigned
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux] (but seen the same issue with 2.3 and 2.1)
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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I'm just creating a single ticket for these issues, I guess they're actually all the same (I've seen weakref uses weakmap, not sure about define_finalizer).

```ruby
require 'weakref'

map = ObjectSpace::WeakMap.new

o = Object.new
o.freeze

begin
  WeakRef.new(o)
rescue => e
  STDERR.puts e
end

begin
  map[o] = 'foo'
rescue => e
  STDERR.puts e
end

begin
  map['bar'] = o
rescue => e
  STDERR.puts e
end

begin
  ObjectSpace.define_finalizer(o, ->(id) { p id })
rescue => e
  STDERR.puts e
end
```

Every statement here raises the runtime error "can't modify frozen Object". The documentation doesn't mention that frozen objects are not allowed, the closest reference we get is a short paragraph in WeakRef: "With this you will have to limit your self to String keys, otherwise you will get an ArgumentError because WeakRef cannot create a finalizer for a Symbol. Symbols are immutable and cannot be garbage collected"



-- 
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