From: "esad (Esad Hajdarevic) via ruby-core" <ruby-core@...>
Date: 2024-04-24T11:00:10+00:00
Subject: [ruby-core:117679] [Ruby master Feature#20444] Kernel#loop: returning the "result" value of StopIteration doesn't work when raised directly

Issue #20444 has been updated by esad (Esad Hajdarevic).


ufuk (Ufuk Kayserilioglu) wrote in #note-7:
> @esad If you just want to return a result from the `loop`, you can use `break <value>` to do that:
> ```
> $ ruby -e "puts loop { break 3 }"
> 3

Calling break from a block passed to a ractor will raise an exception. I think some sample code about my example will be helpful:

Let's make a ractor that just calls all blocks passed to it in a loop:

```
r = Ractor.new do 
  block = Ractor.receive
  loop { block.call() }
end
```

Now let's send it a block that raises StopIteration:

```
block = true.instance_eval { proc { raise StopIteration, 3 } } # instance_eval in true gives us a "shareable" proc 
r.send Ractor.make_shareable(block)
r.take # => nil
```

Let's try with a subclass (this works)

```
class MyStop < ::StopIteration
  attr_reader :result
  def initialize(result)
    @result = result
  end
end

block = true.instance_eval { proc { raise MyStop, 3 } }
r.send Ractor.make_shareable(block)
r.take # => 3
```




----------------------------------------
Feature #20444: Kernel#loop: returning the "result" value of StopIteration doesn't work when raised directly
https://bugs.ruby-lang.org/issues/20444#change-108089

* Author: esad (Esad Hajdarevic)
* Status: Feedback
----------------------------------------
There was a https://bugs.ruby-lang.org/issues/11498 a while ago which was merged in, but I was surprised to find out that raising `StopIteration` in a loop like

`loop { raise StopIteration.new(3) }`

returns nil and not 3.





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