[ruby-core:107187] [Ruby master Feature#18408] Allow pattern match to set instance variables

Issue #18408 has been updated by Dan0042 (Daniel DeLorme).


An additional assignment is too slow?? A few bytes on the stack is too much?? I hope we worry about having meaningful semantics before such premature micro-optimization. Because I do agree that "the behavior is whatever CRuby currently does, and with enough time people depend on it."

Having the value of the variable change even though the pattern doesn't match is unlike anything in ruby. It's as if `"ab" =~  /(a)(c)/` resulted in `$1 == "a"` even though the regexp doesn't match. It makes sense only if you understand the implementation details of the pattern match. From a conceptual viewpoint, I find this behavior very weird.

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Feature #18408: Allow pattern match to set instance variables
https://bugs.ruby-lang.org/issues/18408#change-96047

* Author: Dan0042 (Daniel DeLorme)
* Status: Assigned
* Priority: Normal
* Assignee: ktsj (Kazuki Tsujimoto)
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I expected this to work:

```ruby
42 => @v
```

But instead it raises "syntax error, unexpected instance variable"

Is this intentional?



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