class RuboCop::Cop::Performance::ReverseFirst

This cop identifies places where `reverse.first(n)` and `reverse.first` can be replaced by `last(n).reverse` and `last`.

@example

# bad
array.reverse.first(5)
array.reverse.first

# good
array.last(5).reverse
array.last

Constants

MSG
RESTRICT_ON_SEND

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/performance/reverse_first.rb, line 30
def on_send(node)
  reverse_first_candidate?(node) do |receiver|
    range = correction_range(receiver, node)
    message = build_message(node)

    add_offense(range, message: message) do |corrector|
      replacement = build_good_method(node)

      corrector.replace(range, replacement)
    end
  end
end

Private Instance Methods

build_bad_method(node) click to toggle source
# File lib/rubocop/cop/performance/reverse_first.rb, line 63
def build_bad_method(node)
  if node.arguments?
    "reverse.first(#{node.arguments.first.source})"
  else
    'reverse.first'
  end
end
build_good_method(node) click to toggle source
# File lib/rubocop/cop/performance/reverse_first.rb, line 55
def build_good_method(node)
  if node.arguments?
    "last(#{node.arguments.first.source}).reverse"
  else
    'last'
  end
end
build_message(node) click to toggle source
# File lib/rubocop/cop/performance/reverse_first.rb, line 49
def build_message(node)
  good_method = build_good_method(node)
  bad_method = build_bad_method(node)
  format(MSG, good_method: good_method, bad_method: bad_method)
end
correction_range(receiver, node) click to toggle source
# File lib/rubocop/cop/performance/reverse_first.rb, line 45
def correction_range(receiver, node)
  range_between(receiver.loc.selector.begin_pos, node.loc.expression.end_pos)
end