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Bug #18243

Updated by Eregon (Benoit Daloze) about 3 years ago

```ruby 
 class C 
   attr_accessor :foo 
   def setter_proc 
     Ractor.make_shareable(-> v { @foo = v }) 
   end 
 end 

 c = C.new 
 c.foo = 1 
 p c 
 proc = c.setter_proc 
 p c.frozen? 
 Ractor.new(proc) { |s| s.call(42) }.take 
 p c 
 ``` 
 gives 
 ``` 
 #<C:0x00007f2a3aae7a98 @foo=1> 
 false 
 #<C:0x00007f2a3aae7a98 @foo=42> # BUG 
 ``` 

 But that must be a bug, it means the non-main Ractor can directly mutate an object from the main Ractor. 

 I found this while thinking about https://github.com/ruby/ostruct/pull/29/files and 
 whether `Ractor.make_shareable` would freeze `@table` and the `OpenStruct` instance (I think it needs to). 

 Repro code for ostruct and changing ostruct.rb to `$setter = ::Ractor.make_shareable(setter_proc)`: 
 ```ruby 
 require 'ostruct' 

 os = OpenStruct.new 
 os.foo = 1 

 $setter.call(2) 
 p os 

 Ractor.new($setter) { |s| s.call(42) }.take 
 p os 
 ``` 
 gives 
 ``` 
 #<OpenStruct foo=2> 
 <internal:ractor>:267: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. 
 #<OpenStruct foo=42> # BUG 
 ```

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