From: "jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date: 2023-12-15T20:20:08+00:00
Subject: [ruby-core:115756] [Ruby master Feature#18083] Capture error in ensure block.

Issue #18083 has been updated by jeremyevans0 (Jeremy Evans).


ioquatix (Samuel Williams) wrote in #note-29:
> In the first instance, the question we need to answer is: "Is there a valid use case for $! (assuming dynamic scope as proposed) that isn't better addressed using existing techniques?".
> 
> If the answer is YES, we should implement it.
> 
> If the answer is NO, we should deprecate and remove `$!`.

This perspective ignores backwards compatibility.  If the answer is NO, we would still need to determine if the benefit of removing `$!` exceeds the cost of the loss of backwards compatibility.

----------------------------------------
Feature #18083: Capture error in ensure block.
https://bugs.ruby-lang.org/issues/18083#change-105694

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
As discussed in https://bugs.ruby-lang.org/issues/15567 there are some tricky edge cases.

As a general model, something like the following would be incredibly useful:

``` ruby
begin
 ...
ensure => error
  pp "error occurred" if error
end
```

Currently you can get similar behaviour like this:

``` ruby
begin
  ...
rescue Exception => error
  raise
ensure
  pp "error occurred" if error
end
```

The limitation of this approach is it only works if you don't need any other `rescue` clause. Otherwise, it may not work as expected or require extra care. Also, Rubocop will complain about it.

Using `$!` can be buggy if you call some method from `rescue` or `ensure` clause, since it would be set already. It was discussed extensively in https://bugs.ruby-lang.org/issues/15567 if you want more details.



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