Feature #17724: Make the pin operator support instance/class/global variables

• Status: Closed
• Assignee: ktsj (Kazuki Tsujimoto)
• Target version: -

[jnchito (Junichi Ito)]

When I use pattern match with instance variables, I get an error message like "expecting local variable or method"

@n = 1
case 1
in ^@n
  # ...
end
#=> syntax error, unexpected instance variable, expecting local variable or method (SyntaxError)
#   in ^@n
#       ^~

However using method is not allowed, either.

def n = 1
case 1
in ^n
  # ...
end
#=> n: no such local variable (SyntaxError)

I think the message "expecting local variable or method" is confusing and should be fixed like "expecting local variable."

[marcandre (Marc-Andre Lafortune)]

Agreed. Ideally instance variable would be allowed, no?

[ktsj (Kazuki Tsujimoto)]

• Status changed from Open to Assigned
• Assignee set to ktsj (Kazuki Tsujimoto)

[jeremyevans0 (Jeremy Evans)]

I've added a pull request to directly support instance/class/global variables with the pin operator: https://github.com/ruby/ruby/pull/4502

You could already use all of those variables with the pin expression support by surrounding them in parantheses. However, since local variables and constants are supported, I think it makes sense to also support instance/class/global variables directly. I don't think it makes sense to support methods, as doing so is much more complex (arguments/blocks). Users can use the pin expression support for methods.

My approach to fixing this bug is really introducing a new feature so the bug reported (confusing error message) isn't a problem anymore. Since this changes the pattern matching syntax, it probably should be approved by both @ktsj (Kazuki Tsujimoto) and @matz (Yukihiro Matsumoto)).

[ktsj (Kazuki Tsujimoto)]

• Tracker changed from Bug to Feature
• Subject changed from Pattern matching error message is confusing to Make the pin operator support instance/class/global variables
• ruby -v deleted (ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin20])
• Backport deleted (2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN)

I think it makes sense to also support instance/class/global variables directly.

I agree.

What do you think, @matz (Yukihiro Matsumoto)?

[matz (Yukihiro Matsumoto)]

Sounds reasonable. Accepted.

Matz.

• Status changed from Assigned to Closed

Applied in changeset git|fa87f72e1e84e2b55516be188f00434a683b924c.

---

Add pattern matching pin support for instance/class/global variables

Pin matching for local variables and constants is already supported,
and it is fairly simple to add support for these variable types.

Note that pin matching for method calls is still not supported
without wrapping in parentheses (pin expressions). I think that's
for the best as method calls are far more complex (arguments/blocks).

Implements [Feature #17724]