Bug #16344: Can be assigned to numbered parameter when after used _1

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.0dev (2019-11-11T23:39:38Z trunk 2407e89725) [x86_64-linux]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
• Tags: core

[osyo (manga osyo)]

Steps to reproduce

1. Define local variable _1 outside block
2. Call Numbered parameter in block
3. Assign for _1

Expected behavior

_1 = :local_variable
proc {
  _1
  # Error: Can't assign to numbered parameter _1
  _1 = 42
}

Actual behavior

_1 = :local_variable
proc {
  _1
  # No error
  _1 = 42
}

Cannot be assinged to numbered parameter from #16293.
However, can be assinged to numbered parameter if defined local variable _1 outside block.
I think this is a bug.

[osyo (manga osyo)]

• Description updated (diff)

[Hanmac (Hans Mackowiak)]

i think this has something to do with that _* parameter doesn't cause duplicate syntax errors:

def abc(_x,_x)
  p _x
end

abc("y","z") #=> "y"

See some of your examples from #16293

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

Assigning to the numbered parameter is now a SyntaxError even if it is a local variable in scope, so current master has your expected behavior.

Related to this, accessing the numbered parameter inside a block in master accesses the numbered parameter, even if a local variable of the same name exists in the outer scope:

_1 = :local_variable
proc{_1}.call(:block_arg)
# 2.7: => :local_variable
# 3.0: => :block_arg

I think we should make assigning to a numbered parameter a SyntaxError instead of a warning outside of a block (it was a warning in 2.7). I'll submit a feature request for that.