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?, #excluded_file?, #extra_details?, #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_body

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?, directions, double_quotes_acceptable?, double_quotes_required?, effective_column, ends_its_line?, escape_string, first_part_of_call_chain, interpret_string_escapes, line_range, move_pos, needs_escaping?, numeric_range_size, on_node, operator?, parentheses?, parenthesized_call?, range_with_surrounding_comma, range_with_surrounding_space, source_range, strip_quotes, 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 81

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

  new_condition =
    conditions.each_with_object([]) do |condition, correction|
      variable, = *condition
      if variable.respond_to?(:array_type?) && variable.array_type?
        correction << expand_percent_array(variable)
        next
      end

      correction << condition.source
    end
  new_condition = new_condition.join(', ')

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

#on_case(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 65

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