Class: RuboCop::Cop::Performance::CaseWhenSplat

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

Overview

Place ‘when` conditions that use splat at the end of the list of `when` branches.

Ruby has to allocate memory for the splat expansion every time that the ‘case` `when` statement is run. Since Ruby does not support fall through inside of `case` `when`, like some other languages do, the order of the `when` branches does not matter. By placing any splat expansions at the end of the list of `when` branches we will reduce the number of times that memory has to be allocated for the expansion.

This is not a guaranteed performance improvement. If the data being processed by the ‘case` condition is normalized in a manner that favors hitting a condition in the splat expansion, it is possible that moving the splat condition to the end will use more memory, and run slightly slower.

Examples:

# bad
case foo
when *condition
  bar
when baz
  foobar
end

case foo
when *[1, 2, 3, 4]
  bar
when 5
  baz
end

# good
case foo
when baz
  foobar
when *condition
  bar
end

case foo
when 1, 2, 3, 4
  bar
when 5
  baz
end

Constant Summary collapse

MSG = 
'Place `when` conditions with a splat ' \
'at the end of the `when` branches.'.freeze
ARRAY_MSG = 
'Do not expand array literals in `when` conditions.'.freeze
PERCENT_W = 
'%w'.freeze
PERCENT_CAPITAL_W = 
'%W'.freeze
PERCENT_I = 
'%i'.freeze
PERCENT_CAPITAL_I = 
'%I'.freeze

Constants included from AutocorrectAlignment

AutocorrectAlignment::SPACE

Constants included from Util

Util::ASGN_NODES, Util::BYTE_ORDER_MARK, Util::EQUALS_ASGN_NODES, Util::LITERAL_REGEX, Util::OPERATOR_METHODS, Util::SHORTHAND_ASGN_NODES

Instance Attribute Summary

Attributes inherited from Cop

#config, #corrections, #offenses, #processed_source

Instance Method Summary collapse

Methods included from AutocorrectAlignment

#check_alignment, #configured_indentation_width, #display_column, #indentation, #offset

Methods inherited from Cop

#add_offense, all, #config_to_allow_offenses, #config_to_allow_offenses=, #cop_config, cop_name, #cop_name, cop_type, #correct, #debug?, #details, #display_cop_names?, #display_style_guide?, #duplicate_location?, #excluded_file?, #extra_details?, #find_location, #highlights, inherited, #initialize, #join_force?, lint?, match?, #message, #messages, non_rails, #parse, qualified_cop_name, #reference_url, #relevant_file?, #style_guide_url, #target_ruby_version

Methods included from 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_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

#autocorrect(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 80

def autocorrect(node)
  *conditions, _body = *node

  lambda do |corrector|
    if needs_reorder?(node)
      reorder_condition(corrector, node, replacement(conditions))
    else
      inline_fix_branch(corrector, node, conditions,
                        replacement(conditions))
    end
  end
end

#on_case(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 64

def on_case(node)
  _case_branch, *when_branches, _else_branch = *node
  when_conditions =
    when_branches.each_with_object([]) do |branch, conditions|
      *condition, _ = *branch
      condition.each { |c| conditions << c }
    end

  splat_offenses(when_conditions).reverse_each do |condition|
    range = condition.parent.loc.keyword.join(condition.source_range)
    variable, = *condition
    message = variable.array_type? ? ARRAY_MSG : MSG
    add_offense(condition.parent, range, message)
  end
end