Issue #17145 has been updated by marcandre (Marc-Andre Lafortune).


Maybe we can start with `Ractor.shareable(obj)`?

The major reason why we need it is that there is no way to create a Ractor sharable recursive structure currently.

```ruby
child = {type: :foo}
node = {type: bar, children: [child].freeze}.freeze
child[:parent] = node
child.freeze
```

At this point, everything is frozen, but neither child nor node are Ractor sharable.

`Ractor.shareable(node)` would check for this, and set both `node` and `child`'s "shareable" flag; after that `Ractor.shareable?(node)` would return true.

API-wise, `Ractor.shareable(node)` might be a good start, or `node.freeze(shareable: true)`, or `node.deep_freeze`

----------------------------------------
Feature #17145: Ractor-aware `Object#deep_freeze`
https://bugs.ruby-lang.org/issues/17145#change-87868

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
----------------------------------------
I'd like to propose `Object#deep_freeze`:

Freezes recursively the contents of the receiver (by calling `deep_freeze`) and
then the receiver itself (by calling `freeze`).
Values that are shareable via `Ractor` (e.g. classes) are never frozen this way.

```ruby
# freezes recursively:
ast = [:hash, [:pair, [:str, 'hello'], [:sym, :world]]].deep_freeze
ast.dig(1, 1) # => [:str, 'hello']
ast.dig(1, 1).compact! # => FrozenError

# does not freeze classes:
[[String]].deep_freeze
String.frozen? # => false

# calls `freeze`:
class Foo
  def freeze
    build_cache!
    puts "Ready for freeze"
    super
  end
  # ...
end
[[[Foo.new]]].deep_freeze # => Outputs "Ready for freeze"
```


I think a variant `deep_freeze!` that raises an exception if the result isn't Ractor-shareable would be useful too:

```ruby
class Fire
  def freeze
    # do not call super
  end
end

x = [Fire.new]
x.deep_freeze! # => "Could not be deeply-frozen: #<Fire:0x00007ff151994748>"
```



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