class RuboCop::Cop::Lint::NumberedParameterAssignment


non_numbered_parameter_name = :value
# good
_1 = :value
# bad
@example
as well to prevent confusion.
NOTE: The parametered parameters are from ‘_1` to `_9`. This cop checks `_0`, and over `_10`
-e:1: _1 is reserved for numbered parameter
ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin19]
$ ruby -ve ’_1 = :value’
Assigning to a numbered parameter (from ‘_1` to `_9`) causes an error in Ruby 3.0.
-e:1: warning: `_1’ is reserved for numbered parameter; consider another name
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin19]
$ ruby -ve ‘_1 = :value’
It emulates the following warning in Ruby 2.7:
Checks for uses of numbered parameter assignment.

def on_lvasgn(node) 

def on_lvasgn(node)
  lhs, _rhs = *node
  return unless /\A_(\d+)\z/ =~ lhs
  number = Regexp.last_match(1).to_i
  template = NUMBERED_PARAMETER_RANGE.include?(number) ? NUM_PARAM_MSG : LVAR_MSG
  add_offense(node, message: format(template, number: number))
end