From: marcandre-ruby-core@...
Date: 2020-10-20T21:42:19+00:00
Subject: [ruby-core:100460] [Ruby master Feature#17145] Ractor-aware	`Object#deep_freeze`

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


Eregon (Benoit Daloze) wrote in #note-19:
> Is there a concrete case where it is problematic to not call user's `freeze`?

I thought I [already answered that](https://bugs.ruby-lang.org/issues/17145#note-18), but here's a short example:

```ruby
def Stats
  # ...

  def freeze
    extended_results # build cache if need be
    super
  end

  def extended_results
    @extended_results_cache ||= calc_extended_results
  end

  private
  def calc_extended_results
    # lots of calculations
  end
end
```

There is currently no way for `#frozen?` to be `true` (and `@instance ||= ` to fail) without going through the `#freeze` method. I think we should not break that, especially if there is no callback mechanism to circumvent this.


----------------------------------------
Feature #17145: Ractor-aware `Object#deep_freeze`
https://bugs.ruby-lang.org/issues/17145#change-88079

* 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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