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

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

Overview

Reordering `when` conditions with a splat to the end of the `when` branches can improve performance.

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 should 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. The exception to this is if multiple of your `when` conditions can be true for any given condition. A likely scenario for this defining a higher level when condition to override a condition that is inside of the splat 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 =
'Reordering `when` conditions with a splat to the end ' \
'of the `when` branches can improve performance.'.freeze
ARRAY_MSG =
'Pass the contents of array literals ' \
'directly to `when` conditions.'.freeze

Constants included from Util

Util::LITERAL_REGEX

Instance Attribute Summary

Attributes inherited from Cop

#config, #corrections, #offenses, #processed_source

Instance Method Summary collapse

Methods inherited from Cop

#add_offense, all, autocorrect_incompatible_with, 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_rails_version, #target_ruby_version

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 AST::Sexp

#s

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?, comment_line?, double_quotes_required?, escape_string, first_part_of_call_chain, interpret_string_escapes, line_range, needs_escaping?, on_node, parentheses?, same_line?, to_string_literal, to_supported_styles, tokens

Methods included from PathUtil

absolute?, hidden_dir?, hidden_file_in_not_hidden_dir?, match_path?, pwd, relative_path, reset_pwd, smart_path

Constructor Details

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

Instance Method Details

#autocorrect(when_node) ⇒ Object



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# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 76

def autocorrect(when_node)
  lambda do |corrector|
    if needs_reorder?(when_node)
      reorder_condition(corrector, when_node)
    else
      inline_fix_branch(corrector, when_node)
    end
  end
end

#on_case(case_node) ⇒ Object



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

def on_case(case_node)
  when_conditions = case_node.when_branches.flat_map(&:conditions)

  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, location: range, message: message)
  end
end