class RuboCop::Cop::Performance::FlatMap

1, 2, 3, 4].collect { |e| [e, e

}.flatten
[1, 2, 3, 4].map { |e| [e, e] }.flatten
[1, 2, 3, 4].flat_map { |e| [e, e] }
# good
[1, 2, 3, 4].collect { |e| [e, e] }.flatten(1)
[1, 2, 3, 4].map { |e| [e, e] }.flatten(1)
# bad
@example
This cop is used to identify usages of

def autocorrect(node) 

def autocorrect(node)
  receiver, _flatten, flatten_param = *node
  flatten_level, = *flatten_param
  return if flatten_level.nil?
  array, = *receiver
  lambda do |corrector|
    range = Parser::Source::Range.new(node.loc.expression.source_buffer,
                                      node.loc.dot.begin_pos,
                                      node.loc.expression.end_pos)
    corrector.remove(range)
    corrector.replace(array.loc.selector, 'flat_map')
  end
end

def on_send(node) 

def on_send(node)
  left, second_method, flatten_param = *node
  return unless FLATTEN.include?(second_method)
  flatten_level, = *flatten_param
  expression, = *left
  _array, first_method = *expression
  return unless first_method == :map || first_method == :collect
  message = MSG
  if cop_config['EnabledForFlattenWithoutParams'] && flatten_level.nil?
    message = MSG + FLATTEN_MULTIPLE_LEVELS
  else
    return unless flatten_level == 1
  end
  range = Parser::Source::Range.new(node.loc.expression.source_buffer,
                                    expression.loc.selector.begin_pos,
                                    node.loc.selector.end_pos)
  add_offense(node, range, format(message, first_method, second_method))
end