class RuboCop::Cop::Performance::Detect

This cop is used to identify usages of `first`, `last`, `[0]` or `[-1]` chained to `select`, `find_all` or `filter` and change them to use `detect` instead.

@example

# bad
[].select { |item| true }.first
[].select { |item| true }.last
[].find_all { |item| true }.first
[].find_all { |item| true }.last
[].filter { |item| true }.first
[].filter { |item| true }.last
[].filter { |item| true }[0]
[].filter { |item| true }[-1]

# good
[].detect { |item| true }
[].reverse.detect { |item| true }

`ActiveRecord` compatibility: `ActiveRecord` does not implement a `detect` method and `find` has its own meaning. Correcting ActiveRecord methods with this cop should be considered unsafe.

Constants

CANDIDATE_METHODS
INDEX_MSG
INDEX_REVERSE_MSG
MSG
RESTRICT_ON_SEND
REVERSE_MSG

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 49
def on_send(node)
  detect_candidate?(node) do |receiver, second_method, args|
    if second_method == :[]
      index = args
      args = {}
    end

    return unless args.empty?
    return unless receiver

    receiver, _args, body = *receiver if receiver.block_type?
    return if accept_first_call?(receiver, body)

    register_offense(node, receiver, second_method, index)
  end
end

Private Instance Methods

accept_first_call?(receiver, body) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 68
def accept_first_call?(receiver, body)
  caller, _first_method, args = *receiver

  # check that we have usual block or block pass
  return true if body.nil? && (args.nil? || !args.block_pass_type?)

  lazy?(caller)
end
autocorrect(corrector, node, replacement) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 100
def autocorrect(corrector, node, replacement)
  receiver, _first_method = *node

  first_range = receiver.source_range.end.join(node.loc.selector)

  receiver, _args, _body = *receiver if receiver.block_type?

  corrector.remove(first_range)
  corrector.replace(receiver.loc.selector, replacement)
end
lazy?(node) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 126
def lazy?(node)
  return false unless node

  receiver, method, _args = *node
  method == :lazy && !receiver.nil?
end
message_for_method(method, index) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 111
def message_for_method(method, index)
  case method
  when :[]
    index == -1 ? INDEX_REVERSE_MSG : INDEX_MSG
  when :last
    REVERSE_MSG
  else
    MSG
  end
end
preferred_method() click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 122
def preferred_method
  config.for_cop('Style/CollectionMethods')['PreferredMethods']['detect'] || 'detect'
end
register_offense(node, receiver, second_method, index) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 77
def register_offense(node, receiver, second_method, index)
  _caller, first_method, _args = *receiver
  range = receiver.loc.selector.join(node.loc.selector)

  message = message_for_method(second_method, index)
  formatted_message = format(message, prefer: preferred_method,
                                      first_method: first_method,
                                      second_method: second_method,
                                      index: index)

  add_offense(range, message: formatted_message) do |corrector|
    autocorrect(corrector, node, replacement(second_method, index))
  end
end
replacement(method, index) click to toggle source
# File lib/rubocop/cop/performance/detect.rb, line 92
def replacement(method, index)
  if method == :last || method == :[] && index == -1
    "reverse.#{preferred_method}"
  else
    preferred_method
  end
end