[ruby-core:120107] [Ruby master Bug#20931] Using `in` as an expression requires extra parentheses
From:
"alanwu (Alan Wu) via ruby-core" <ruby-core@...>
Date:
2024-12-04 22:46:03 UTC
List:
ruby-core #120107
Issue #20931 has been updated by alanwu (Alan Wu).
Status changed from Open to Rejected
I'm closing this since I'm pretty sure this isn't a bug. An imperfect explanation follows. Feel free to jump in if anyone has a better explanation.
To understand the precedence, note that `in` has a symbolic friend `=>`, and much like how `or` binds lower than `||`, `in` binds lower than `=>`. (Runtime behavior of `=>` and `in` are different, though.)
As for why it requires parentheses in argument context, it's consistent with other single word English keywords such as `and`, `or`, `if`, and `unless`:
<details>
```shell
$ for keyword in and or if unless; do ruby -vc -e "puts(1 $keyword 1)"; done
ruby 3.4.0dev (2024-12-04T21:26:31Z master c0e12bf8d2) +PRISM [arm64-darwin24]
ruby: -e:1: syntax errors found (SyntaxError)
> 1 | puts(1 and 1)
| ^~~ unexpected 'and'; expected a `)` to close the arguments
| ^ unexpected ')', ignoring it
| ^ unexpected ')', expecting end-of-input
2 |
ruby 3.4.0dev (2024-12-04T21:26:31Z master c0e12bf8d2) +PRISM [arm64-darwin24]
ruby: -e:1: syntax errors found (SyntaxError)
> 1 | puts(1 or 1)
| ^~ unexpected 'or'; expected a `)` to close the arguments
| ^ unexpected ')', ignoring it
| ^ unexpected ')', expecting end-of-input
2 |
ruby 3.4.0dev (2024-12-04T21:26:31Z master c0e12bf8d2) +PRISM [arm64-darwin24]
-e:1: warning: literal in condition
ruby: -e:1: syntax errors found (SyntaxError)
> 1 | puts(1 if 1)
| ^~ unexpected 'if'; expected a `)` to close the arguments
| ^ unexpected ')', ignoring it
| ^ unexpected ')', expecting end-of-input
2 |
ruby 3.4.0dev (2024-12-04T21:26:31Z master c0e12bf8d2) +PRISM [arm64-darwin24]
-e:1: warning: literal in condition
ruby: -e:1: syntax errors found (SyntaxError)
> 1 | puts(1 unless 1)
| ^~~~~~ unexpected 'unless'; expected a `)` to close the arguments
| ^ unexpected ')', ignoring it
| ^ unexpected ')', expecting end-of-input
2 |
```
</details>
Allowing these limit examples to work as expected probably causes parsing ambiguity in some other cases, so they're rejected. But I'm no parser expert.
----------------------------------------
Bug #20931: Using `in` as an expression requires extra parentheses
https://bugs.ruby-lang.org/issues/20931#change-110855
* Author: stephenprater (Stephen Prater)
* Status: Rejected
* ruby -v: 3.3.1
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
TBH - I'm not sure if this is a bug or not - but it certainly surprising behavior and I'd at least like to understand it.
Given a hash t - that can be pattern matched: `t = {a: 1, b:1 }`
``` ruby
r = t in {a: 1, c:1 } # returns `false`
r # {a: 1, c: 1} wat
```
Presumably this is because `=` binds higher than `in` - so that expression is equivalent to `(r = t) in {a: 1, c: 1}`
But in that case - why does using the results of `in` require an additional set of parentheses to avoid a syntax error when the result of the expression is used as an argument to a method?
``` ruby
puts(t in {a: 1, c: 1}) # syntax error
puts((t in {a: 1, c: 1}) # false
```
Especially since this works fine:
``` ruby
puts(case t; in { a: 1, c:1 }; true; else false; end)
```
--
https://bugs.ruby-lang.org/
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