[ruby-core:105002] [Ruby master Feature#18083] Capture error in ensure block.

Issue #18083 has been updated by matz (Yukihiro Matsumoto).


I hesitate to enhance `ensure`. It's ugly and against the basic concept of `ensure`.
The `ensure` behavior was taken from `unwind-protect` macro of Lisp, and it does not distinguish between error execution and normal execution. If you check the error condition in the `ensure` clause, especially using `$!`, I doubt you misuse the `ensure` concept.

If you really wanted to check the error condition, you may want to use local variables.

```ruby
begin
  ....
  no_error = true
ensure
  error_handling unless no_error
end
```

At the same time, I may underestimate the pain of OP. Let me think about it for a while.

Matz.


----------------------------------------
Feature #18083: Capture error in ensure block.
https://bugs.ruby-lang.org/issues/18083#change-93402

* 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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