class RuboCop::Cop::Performance::Sum

This cop identifies places where custom code finding the sum of elements in some Enumerable object can be replaced by `Enumerable#sum` method.

This cop can change auto-correction scope depending on the value of `SafeAutoCorrect`. Its auto-correction is marked as safe by default (`SafeAutoCorrect: true`) to prevent `TypeError` in auto-correced code when initial value is not specified as shown below:

source,ruby

['a', 'b'].sum # => (String can't be coerced into Integer)


Therefore if initial value is not specified, unsafe auto-corrected will not occur.

If you always want to enable auto-correction, you can set `SafeAutoCorrect: false`.

source,yaml

Performance/Sum:

SafeAutoCorrect: false

Please note that the auto-correction command line option will be changed from `rubocop -a` to `rubocop -A`, which includes unsafe auto-correction.

@example

# bad
[1, 2, 3].inject(:+)                        # These bad cases with no initial value are unsafe and
[1, 2, 3].inject(&:+)                       # will not be auto-correced by default. If you want to
[1, 2, 3].reduce { |acc, elem| acc + elem } # auto-corrected, you can set `SafeAutoCorrect: false`.
[1, 2, 3].reduce(10, :+)
[1, 2, 3].map { |elem| elem ** 2 }.sum
[1, 2, 3].collect(&:count).sum(10)

# good
[1, 2, 3].sum
[1, 2, 3].sum(10)
[1, 2, 3].sum { |elem| elem ** 2 }
[1, 2, 3].sum(10, &:count)

Constants

MSG
MSG_IF_NO_INIT_VALUE
RESTRICT_ON_SEND

Public Instance Methods

on_block(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 89
def on_block(node)
  sum_with_block_candidate?(node) do |send, init, var_acc, var_elem, body|
    if acc_plus_elem?(body, var_acc, var_elem) || elem_plus_acc?(body, var_elem, var_acc)
      range = sum_block_range(send, node)
      message = build_block_message(send, init, var_acc, var_elem, body)

      add_offense(range, message: message) do |corrector|
        autocorrect(corrector, init, range)
      end
    end
  end
end
on_send(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 82
def on_send(node)
  return if empty_array_literal?(node)

  handle_sum_candidate(node)
  handle_sum_map_candidate(node)
end

Private Instance Methods

array_literal?(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 132
def array_literal?(node)
  receiver = node.children.first
  receiver&.literal? && receiver&.array_type?
end
autocorrect(corrector, init, range) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 137
def autocorrect(corrector, init, range)
  return if init.empty? && safe_autocorrect?

  replacement = build_good_method(init)

  corrector.replace(range, replacement)
end
autocorrect_sum_map(corrector, sum, map, init) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 145
def autocorrect_sum_map(corrector, sum, map, init)
  sum_range = method_call_with_args_range(sum)
  map_range = method_call_with_args_range(map)

  block_pass = map.last_argument if map.last_argument&.block_pass_type?
  replacement = build_good_method(init, block_pass)

  corrector.remove(sum_range)

  dot = '.' if map.receiver
  corrector.replace(map_range, "#{dot}#{replacement}")
end
build_block_bad_method(method, init, var_acc, var_elem, body) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 221
def build_block_bad_method(method, init, var_acc, var_elem, body)
  bad_method = method.to_s

  unless init.empty?
    init = init.first
    bad_method += "(#{init.source})"
  end
  bad_method += " { |#{var_acc}, #{var_elem}| #{body.source} }"
  bad_method
end
build_block_message(send, init, var_acc, var_elem, body) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 188
def build_block_message(send, init, var_acc, var_elem, body)
  good_method = build_good_method(init)
  bad_method = build_block_bad_method(send.method_name, init, var_acc, var_elem, body)
  format(MSG, good_method: good_method, bad_method: bad_method)
end
build_good_method(init, block_pass = nil) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 194
def build_good_method(init, block_pass = nil)
  good_method = 'sum'

  args = []
  unless init.empty?
    init = init.first
    args << init.source unless init.int_type? && init.value.zero?
  end
  args << block_pass.source if block_pass
  good_method += "(#{args.join(', ')})" unless args.empty?
  good_method
end
build_method_bad_method(init, method, operation) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 207
def build_method_bad_method(init, method, operation)
  bad_method = "#{method}("
  unless init.empty?
    init = init.first
    bad_method += "#{init.source}, "
  end
  bad_method += if operation.block_pass_type?
                  '&:+)'
                else
                  ':+)'
                end
  bad_method
end
build_method_message(node, method, init, operation) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 170
def build_method_message(node, method, init, operation)
  good_method = build_good_method(init)
  bad_method = build_method_bad_method(init, method, operation)
  msg = if init.empty? && !array_literal?(node)
          MSG_IF_NO_INIT_VALUE
        else
          MSG
        end
  format(msg, good_method: good_method, bad_method: bad_method)
end
build_sum_map_message(method, init) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 181
def build_sum_map_message(method, init)
  sum_method = build_good_method(init)
  good_method = "#{sum_method} { ... }"
  bad_method = "#{method} { ... }.#{sum_method}"
  format(MSG, good_method: good_method, bad_method: bad_method)
end
empty_array_literal?(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 127
def empty_array_literal?(node)
  receiver = node.children.first
  array_literal?(node) && receiver && receiver.children.empty?
end
handle_sum_candidate(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 104
def handle_sum_candidate(node)
  sum_candidate?(node) do |method, init, operation|
    range = sum_method_range(node)
    message = build_method_message(node, method, init, operation)

    add_offense(range, message: message) do |corrector|
      autocorrect(corrector, init, range)
    end
  end
end
handle_sum_map_candidate(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 115
def handle_sum_map_candidate(node)
  sum_map_candidate?(node) do |map, init|
    next if node.block_literal? || node.block_argument?

    message = build_sum_map_message(map.method_name, init)

    add_offense(sum_map_range(map, node), message: message) do |corrector|
      autocorrect_sum_map(corrector, node, map, init)
    end
  end
end
method_call_with_args_range(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 232
def method_call_with_args_range(node)
  if (receiver = node.receiver)
    receiver.source_range.end.join(node.source_range.end)
  else
    node.source_range
  end
end
sum_block_range(send, node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 166
def sum_block_range(send, node)
  range_between(send.loc.selector.begin_pos, node.loc.end.end_pos)
end
sum_map_range(map, sum) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 162
def sum_map_range(map, sum)
  range_between(map.loc.selector.begin_pos, sum.source_range.end.end_pos)
end
sum_method_range(node) click to toggle source
# File lib/rubocop/cop/performance/sum.rb, line 158
def sum_method_range(node)
  range_between(node.loc.selector.begin_pos, node.loc.end.end_pos)
end