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
OPEN_BRACKET = 
'['.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::BASIC_LITERALS, Util::EQUALS_ASGN_NODES, Util::LITERALS, Util::OPERATOR_METHODS, Util::PROC_NEW_NODE, 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, #indentation, #offset, #start_of_line?

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?, inherited, #initialize, #join_force?, lint?, match?, #message, non_rails, qualified_cop_name, rails?, #reference_url, #relevant_file?, #style_guide_url

Methods included from NodePattern::Macros

#def_node_matcher, #def_node_search

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, command?, comment_line?, const_name, directions, first_part_of_call_chain, lambda?, lambda_or_proc?, line_range, move_pos, numeric_range_size, on_node, operator?, parentheses?, proc?, range_with_surrounding_comma, range_with_surrounding_space, source_range, strip_quotes, within_node?

Methods included from PathUtil

hidden?, issue_deprecation_warning, 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)
  condition, = *node
  variable, = *condition
  if variable.array_type?
    correct_array_literal(condition, variable)
  else
    reorder_splat_condition(node)
  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
      conditions << condition
    end

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