class RuboCop::Cop::Performance::Casecmp

This cop identifies places where a case-insensitive string comparison can better be implemented using `casecmp`. This cop is unsafe because `String#casecmp` and `String#casecmp?` behave differently when using Non-ASCII characters.

@example

# bad
str.downcase == 'abc'
str.upcase.eql? 'ABC'
'abc' == str.downcase
'ABC'.eql? str.upcase
str.downcase == str.downcase

# good
str.casecmp('ABC').zero?
'abc'.casecmp(str).zero?

Constants

CASE_METHODS
MSG
RESTRICT_ON_SEND

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/performance/casecmp.rb, line 50
def on_send(node)
  return unless downcase_eq(node) || eq_downcase(node)
  return unless (parts = take_method_apart(node))

  _receiver, method, arg, variable = parts
  good_method = build_good_method(arg, variable)

  message = format(MSG, good: good_method, bad: node.source)
  add_offense(node, message: message) do |corrector|
    correction(corrector, node, method, arg, variable)
  end
end

Private Instance Methods

build_good_method(arg, variable) click to toggle source
# File lib/rubocop/cop/performance/casecmp.rb, line 90
def build_good_method(arg, variable)
  # We want resulting call to be parenthesized
  # if arg already includes one or more sets of parens, don't add more
  # or if method call already used parens, again, don't add more
  if arg.send_type? || !parentheses?(arg)
    "#{variable.source}.casecmp(#{arg.source}).zero?"
  else
    "#{variable.source}.casecmp#{arg.source}.zero?"
  end
end
correction(corrector, node, method, arg, variable) click to toggle source
# File lib/rubocop/cop/performance/casecmp.rb, line 82
def correction(corrector, node, method, arg, variable)
  corrector.insert_before(node.loc.expression, '!') if method == :!=

  replacement = build_good_method(arg, variable)

  corrector.replace(node.loc.expression, replacement)
end
take_method_apart(node) click to toggle source
# File lib/rubocop/cop/performance/casecmp.rb, line 65
def take_method_apart(node)
  if downcase_downcase(node)
    receiver, method, rhs = *node
    arg, = *rhs
  elsif downcase_eq(node)
    receiver, method, arg = *node
  elsif eq_downcase(node)
    arg, method, receiver = *node
  else
    return
  end

  variable, = *receiver

  [receiver, method, arg, variable]
end