[ruby-core:91457] [Ruby trunk Feature#15567] Allow ensure to match specific situations

Issue #15567 has been updated by matz (Yukihiro Matsumoto).

Status changed from Open to Rejected

The language feature similar to `ensure` can be observed in many languages (`unwind-protocol` in Lisp, `defer` in Go, `finally` in Java and others), but neither of them considers the situation. That indicates there's no real-world use-case for it. So currently I believe there's no benefit enough the implementation cost and making the language more complex.

Matz.


----------------------------------------
Feature #15567: Allow ensure to match specific situations
https://bugs.ruby-lang.org/issues/15567#change-76717

* Author: ioquatix (Samuel Williams)
* Status: Rejected
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Target version: 
----------------------------------------
There are some situations where `rescue Exception` or `ensure` are not sufficient to correctly, efficiently and easily handle abnormal flow control.

Take the following program for example:

```
def doot
	yield
ensure
	# Did the function run to completion?
	return "abnormal" if $!
end

puts doot{throw :foo}
puts doot{raise "Boom"}
puts doot{"Hello World"}

catch(:foo) do
	puts doot{throw :foo}
end
```

Using `rescue Exception` is not sufficient as it is not invoked by `throw`.

Using `ensure` is inefficient because it's triggered every time, even though exceptional case might never happen or happen very infrequently.

I propose some way to limit the scope of the ensure block:

```
def doot
	yield
ensure when raise, throw
	return "abnormal"
end
```

The scope should be one (or more) of `raise`, `throw`, `return`, `next`, `break`, `redo`, `retry` (everything in `enum ruby_tag_type` except all except for `RUBY_TAG_FATAL`).

Additionally, it might be nice to support the inverted pattern, i.e.

```
def doot
	yield
ensure when not return
	return "abnormal"
end
```

Inverted patterns allow user to specify the behaviour without having problems if future scopes are introduced.

`return` in this case matches both explicit and implicit.




-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>