class RuboCop::Cop::Style::ZeroLengthPredicate

Checks for numeric comparisons that can be replaced by a predicate method, such as receiver.length == 0, receiver.length > 0, receiver.length != 0, receiver.length < 1 and receiver.size == 0 that can be replaced by receiver.empty? and !receiver.empty?.

@safety

This cop is unsafe because it cannot be guaranteed that the receiver
has an `empty?` method that is defined in terms of `length`. If there
is a non-standard class that redefines `length` or `empty?`, the cop
may register a false positive.

@example

# bad
[1, 2, 3].length == 0
0 == "foobar".length
array.length < 1
{a: 1, b: 2}.length != 0
string.length > 0
hash.size > 0

# good
[1, 2, 3].empty?
"foobar".empty?
array.empty?
!{a: 1, b: 2}.empty?
!string.empty?
!hash.empty?

Constants

NONZERO_MSG
RESTRICT_ON_SEND
ZERO_MSG

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/style/zero_length_predicate.rb, line 42
def on_send(node)
  check_zero_length_predicate(node)
  check_nonzero_length_predicate(node)
end

Private Instance Methods

check_nonzero_length_predicate(node) click to toggle source
# File lib/rubocop/cop/style/zero_length_predicate.rb, line 64
def check_nonzero_length_predicate(node)
  nonzero_length_predicate = nonzero_length_predicate(node.parent)
  return unless nonzero_length_predicate

  lhs, opr, rhs = nonzero_length_predicate

  return if non_polymorphic_collection?(node.parent)

  add_offense(
    node.parent, message: format(NONZERO_MSG, lhs: lhs, opr: opr, rhs: rhs)
  ) do |corrector|
    corrector.replace(node.parent, replacement(node.parent))
  end
end
check_zero_length_predicate(node) click to toggle source
# File lib/rubocop/cop/style/zero_length_predicate.rb, line 49
def check_zero_length_predicate(node)
  zero_length_predicate = zero_length_predicate(node.parent)
  return unless zero_length_predicate

  lhs, opr, rhs = zero_length_predicate

  return if non_polymorphic_collection?(node.parent)

  add_offense(
    node.parent, message: format(ZERO_MSG, lhs: lhs, opr: opr, rhs: rhs)
  ) do |corrector|
    corrector.replace(node.parent, replacement(node.parent))
  end
end
replacement(node) click to toggle source
# File lib/rubocop/cop/style/zero_length_predicate.rb, line 93
def replacement(node)
  receiver = zero_length_receiver(node)
  return "#{receiver.source}.empty?" if receiver

  "!#{other_receiver(node).source}.empty?"
end