class RuboCop::Cop::Performance::CollectionLiteralInLoop

This cop identifies places where Array and Hash literals are used within loops. It is better to extract them into a local variable or constant to avoid unnecessary allocations on each iteration.

You can set the minimum number of elements to consider an offense with `MinSize`.

@example

# bad
users.select do |user|
  %i[superadmin admin].include?(user.role)
end

# good
admin_roles = %i[superadmin admin]
users.select do |user|
  admin_roles.include?(user.role)
end

# good
ADMIN_ROLES = %i[superadmin admin]
...
users.select do |user|
  ADMIN_ROLES.include?(user.role)
end

Constants

ARRAY_METHODS
ENUMERABLE_METHOD_NAMES
HASH_METHODS
LOOP_TYPES
MSG
NONMUTATING_ARRAY_METHODS
NONMUTATING_HASH_METHODS
POST_CONDITION_LOOP_TYPES

Public Instance Methods

on_send(node) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 80
def on_send(node)
  receiver, method, = *node.children
  return unless check_literal?(receiver, method) && parent_is_loop?(receiver)

  message = format(MSG, literal_class: literal_class(receiver))
  add_offense(receiver, message: message)
end

Private Instance Methods

check_literal?(node, method) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 90
def check_literal?(node, method)
  !node.nil? &&
    nonmutable_method_of_array_or_hash?(node, method) &&
    node.children.size >= min_size &&
    node.recursive_basic_literal?
end
enumerable_method?(method_name) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 130
def enumerable_method?(method_name)
  ENUMERABLE_METHOD_NAMES.include?(method_name)
end
keyword_loop?(type) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 112
def keyword_loop?(type)
  LOOP_TYPES.include?(type)
end
literal_class(node) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 122
def literal_class(node)
  if node.array_type?
    'Array'
  elsif node.hash_type?
    'Hash'
  end
end
loop?(ancestor, node) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 106
def loop?(ancestor, node)
  keyword_loop?(ancestor.type) ||
    kernel_loop?(ancestor) ||
    node_within_enumerable_loop?(node, ancestor)
end
min_size() click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 134
def min_size
  Integer(cop_config['MinSize'] || 1)
end
node_within_enumerable_loop?(node, ancestor) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 116
def node_within_enumerable_loop?(node, ancestor)
  enumerable_loop?(ancestor) do |receiver|
    receiver != node && !receiver&.descendants&.include?(node)
  end
end
nonmutable_method_of_array_or_hash?(node, method) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 97
def nonmutable_method_of_array_or_hash?(node, method)
  (node.array_type? && ARRAY_METHODS.include?(method)) ||
    (node.hash_type? && HASH_METHODS.include?(method))
end
parent_is_loop?(node) click to toggle source
# File lib/rubocop/cop/performance/collection_literal_in_loop.rb, line 102
def parent_is_loop?(node)
  node.each_ancestor.any? { |ancestor| loop?(ancestor, node) }
end