Class: RuboCop::Cop::Performance::Count

Inherits:
Cop
  • Object
show all
Includes:
SafeMode
Defined in:
lib/rubocop/cop/performance/count.rb

Overview

This cop is used to identify usages of count on an Enumerable that follow calls to select or reject. Querying logic can instead be passed to the count call.

ActiveRecord compatibility: ActiveRecord will ignore the block that is passed to count. Other methods, such as select, will convert the association to an array and then run the block on the array. A simple work around to make count work with a block is to call ‘to_a.count …`.

Example:

Model.where(id: [1, 2, 3].select { |m| m.method == true }.size

becomes:

Model.where(id: [1, 2, 3]).to_a.count { |m| m.method == true }

Examples:

# bad
[1, 2, 3].select { |e| e > 2 }.size
[1, 2, 3].reject { |e| e > 2 }.size
[1, 2, 3].select { |e| e > 2 }.length
[1, 2, 3].reject { |e| e > 2 }.length
[1, 2, 3].select { |e| e > 2 }.count { |e| e.odd? }
[1, 2, 3].reject { |e| e > 2 }.count { |e| e.even? }
array.select(&:value).count

# good
[1, 2, 3].count { |e| e > 2 }
[1, 2, 3].count { |e| e < 2 }
[1, 2, 3].count { |e| e > 2 && e.odd? }
[1, 2, 3].count { |e| e < 2 && e.even? }
Model.select('field AS field_one').count
Model.select(:value).count

Constant Summary collapse

MSG = 
'Use `count` instead of `%s...%s`.'.freeze

Constants included from Util

Util::ASGN_NODES, Util::BYTE_ORDER_MARK, Util::CONDITIONAL_NODES, Util::EQUALS_ASGN_NODES, Util::LITERAL_REGEX, Util::LOGICAL_OPERATOR_NODES, Util::MODIFIER_NODES, Util::OPERATOR_METHODS, Util::SHORTHAND_ASGN_NODES

Instance Attribute Summary

Attributes inherited from Cop

#config, #corrections, #offenses, #processed_source

Instance Method Summary collapse

Methods inherited from Cop

#add_offense, all, badge, #config_to_allow_offenses, #config_to_allow_offenses=, #cop_config, #cop_name, cop_name, #correct, department, #duplicate_location?, #excluded_file?, #find_location, #highlights, inherited, #initialize, #join_force?, lint?, match?, #message, #messages, non_rails, #parse, qualified_cop_name, #relevant_file?, #target_ruby_version

Methods included from AST::Sexp

#s

Methods included from NodePattern::Macros

#def_node_matcher, #def_node_search, #node_search, #node_search_all, #node_search_body, #node_search_first

Methods included from AutocorrectLogic

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #support_autocorrect?

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

begins_its_line?, block_length, comment_line?, compatible_external_encoding_for?, directions, double_quotes_acceptable?, double_quotes_required?, effective_column, ends_its_line?, escape_string, first_part_of_call_chain, hard_to_type?, interpret_string_escapes, line_distance, line_range, move_pos, needs_escaping?, numeric_range_size, on_node, operator?, parentheses?, parenthesized_call?, preceed?, range_between, range_with_surrounding_comma, range_with_surrounding_space, same_line?, source_range, strip_quotes, stripped_source_upto, to_string_literal, to_supported_styles, to_symbol_literal, within_node?

Methods included from PathUtil

absolute?, match_path?, relative_path

Constructor Details

This class inherits a constructor from RuboCop::Cop::Cop

Instance Method Details

#on_send(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/count.rb', line 52

def on_send(node)
  return if rails_safe_mode?

  count_candidate?(node) do |selector_node, selector, counter|
    return unless eligible_node?(node)

    range = source_starting_at(node) do
      selector_node.loc.selector.begin_pos
    end

    add_offense(node, range, format(MSG, selector, counter))
  end
end