From: shout@...
Date: 2019-06-20T19:17:25+00:00
Subject: [ruby-core:93286] [Ruby trunk Feature#15936] on_error in lieu of	rescue, raise

Issue #15936 has been updated by kylemacey (Kyle Macey).


jeremyevans0 (Jeremy Evans) wrote:
> kylemacey (Kyle Macey) wrote:
> > What would be a thought on using another keyword that doesn't actually _rescue_ an exception, but performs an operation in the event of an error? Similar to `ensure`, but only in the event of an error.
> > 
> > ```
> > begin
> >   some_method
> > on_error StandardError
> >   job.fail! 
> > end
> > ```
> 
> Thankfully, Ruby already supports what you want:
> 
> ```ruby
> begin
>   some_method
> ensure
>   job.fail! if $! # or use case $! if you want to handle specific exception classes differently
> end
> ```
> 
> As you can already accomplish this with current Ruby syntax, I do not think adding a keyword for it is warranted.

`ensure` fires even if there is no exception. This keyword would only fire when there is an exception. In your example, `job.fail!` would always be called.

----------------------------------------
Feature #15936: on_error in lieu of rescue, raise
https://bugs.ruby-lang.org/issues/15936#change-78754

* Author: kylemacey (Kyle Macey)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
A common bad pattern in ruby is to rescue any exception and accidentally clobber the exception. 

```
begin
  some_method
rescue StandardError
  # 
end
```

Most linters will complain if you write rescues like the code above. However, this could be useful if we want to perform an operation on _any_ error, as long as we re-raise the exception after doing our work.

```
begin
  some_method
rescue StandardError
  job.fail! 
  raise
end
```

Here, though, we run the risk of potentially forgetting to reraise the exception, or having to make exceptions in our linter for an operation that is overall benign.

What would be a thought on using another keyword that doesn't actually _rescue_ an exception, but performs an operation in the event of an error? Similar to `ensure`, but only in the event of an error.

```
begin
  some_method
on_error StandardError
  job.fail! 
end
```

(obviously, someone more creative than me should come up with a better name)



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