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 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?, 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, trim_string_interporation_escape_character

Methods included from PathUtil

absolute?, chdir, 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