From: "byroot (Jean Boussier)" <noreply@...>
Date: 2021-09-17T14:51:11+00:00
Subject: [ruby-core:105329] [Ruby master Feature#18148] Marshal.load freeze	option

Issue #18148 has been updated by byroot (Jean Boussier).


I implemented a patch https://github.com/ruby/ruby/pull/4859

NB: it does include some extra fixes for https://bugs.ruby-lang.org/issues/18141#change-93742, because the implementation wouldn't have been possible without.

----------------------------------------
Feature #18148: Marshal.load freeze option
https://bugs.ruby-lang.org/issues/18148#change-93744

* Author: byroot (Jean Boussier)
* Status: Assigned
* Priority: Normal
----------------------------------------
### Behavior

If passed `freeze: true`, all the deserialized objects should be frozen, and if possible, strings should be deduped.

This is similar to the `freeze` option recently added to `JSON` (https://github.com/flori/json/pull/447), `Psych` (https://github.com/ruby/psych/pull/414) and `MessagePack` (https://github.com/msgpack/msgpack-ruby/pull/194).

### Use cases

This option is useful in many scenarios:

  - If the deserialized data is meant to stay on the heap for the lifetime of the program, the string deduplication reduce the memory overhead, and all objects being frozen improve copy on write and ensure that static data isn't accidentally mutated.
  - If the deserialized data is used in a memory cache or similar, deep freezing it protect against mutation and allow to return the value directly without first deep cloning it.
  - While not very performant, it can be used as a `deep_freeze` mechanism with `Marshal.load(Marshal.dump(object), freeze: true)`.



### Snippets


```ruby
payload = Marshal.dump({"foo" => ["bar"]})
object = Marshal.load(payload, freeze: true)

object.frozen?
object.dig("foo").frozen?
object.dig("foo", 1).frozen?


Marshal.load(payload, ->(obj) { raise "unexpected" unless obj.frozen? }, freeze: true)
```


```ruby
def cache_get(key)
  if entry = in_memory_cache.get(key)
    return entry
  end

  if payload = network_cache.get(key)
    object = Marshal.load(payload, freeze: true)
    in_memory_cache.set(key, object) # if the object tree wasn't frozen, we'd need to deep dup to avoid mutation.
    object
  end
end
```



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