Issue #12214 has been reported by Martin Tournoij.

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Feature #12214: Inconsistent behaviour and lack of warnings/errors when referencing duplicated _variables
https://bugs.ruby-lang.org/issues/12214

* Author: Martin Tournoij
* Status: Open
* Priority: Normal
* Assignee: 
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	_, _ = [1, 2]
	p _

gives `2`

	def foo _, _
		p _
	end
	foo 1, 2

gives `1`

	def foo _, _=2
		p _
	end
	foo 1

gives `2`

In other words, referencing duplicated variables starting with an underscore gives inconsistent results.

In the first example it makes since since it's basically:

    _ = 1
    _ = 2

In the method it makes a bit less sense, especially since the behaviour is inconsistent.

My suggested fix would be to at least make referencing duplicated _variables a warning with `ruby -w`. Perhaps it also makes sense to do this for *all* _variables, since the underscore indicates you should not reference them...

It could, perhaps, even me made an error to reference duplicated variables like this. The behaviour is surprising, and likely to change in future versions of Ruby...




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