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

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, AutoCorrector, Base
Instance Chain:
self, RangeHelp, Alignment, Base
Inherits: Base
  • Object
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.

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

Cop Safety Information:

  • This cop is not unsafe autocorrection because it 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. See for more details: https://github.com/rubocop/rubocop/pull/6163

Constant Summary

Instance Method Summary

Instance Method Details

#autocorrect(corrector, when_node) (private)

[ GitHub ] 

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 83



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


  








  

    #indent_for(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 140



def indent_for(node)
  ' ' * node.loc.column
end


  








  

    #inline_fix_branch(corrector, when_node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 100



def inline_fix_branch(corrector, when_node)
  conditions = when_node.conditions
  range = range_between(conditions[0].source_range.begin_pos, conditions[-1].source_range.end_pos)

  corrector.replace(range, replacement(conditions))
end


  








  

    #needs_reorder?(when_node)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 164



def needs_reorder?(when_node)
  following_branches = when_node.parent.when_branches[(when_node.branch_index + 1)..]

  following_branches.any? do |when_branch|
    when_branch.conditions.any? do |condition|
      non_splat?(condition)
    end
  end
end


  








  

    #new_branch_without_then(node, new_condition)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 136



def new_branch_without_then(node, new_condition)
  "\n#{indent_for(node)}when #{new_condition}\n#{indent_for(node.body)}#{node.body.source}"
end


  








  

    #new_condition_with_then(node, new_condition)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 132



def new_condition_with_then(node, new_condition)
  "\n#{indent_for(node)}when #{new_condition} then #{node.body.source}"
end


  








  

    #non_splat?(condition)  ⇒ Boolean  (private)
  



  

    
  





  


  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 158



def non_splat?(condition)
  variable, = *condition

  (condition.splat_type? && variable.array_type?) || !condition.splat_type?
end


  








  

    #on_case(case_node)  
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 66



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

  splat_offenses(when_conditions).reverse_each do |condition|
    next if ignored_node?(condition.parent)

    ignore_node(condition.parent)
    variable, = *condition
    message = variable.array_type? ? ARRAY_MSG : MSG
    add_offense(range(condition), message: message) do |corrector|
      autocorrect(corrector, condition.parent)
    end
  end
end


  








  

    #range(node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 91



def range(node)
  node.parent.loc.keyword.join(node.source_range)
end


  








  

    #reorder_condition(corrector, when_node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 107



def reorder_condition(corrector, when_node)
  when_branches = when_node.parent.when_branches

  return if when_branches.one?

  corrector.remove(when_branch_range(when_node))
  corrector.insert_after(when_branches.last, reordering_correction(when_node))
end


  








  

    #reordering_correction(when_node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 116



def reordering_correction(when_node)
  new_condition = replacement(when_node.conditions)

  if same_line?(when_node, when_node.body)
    new_condition_with_then(when_node, new_condition)
  else
    new_branch_without_then(when_node, new_condition)
  end
end


  








  

    #replacement(conditions)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 95



def replacement(conditions)
  reordered = conditions.partition(&:splat_type?).reverse
  reordered.flatten.map(&:source).join(', ')
end


  








  

    #splat_offenses(when_conditions)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 144



def splat_offenses(when_conditions)
  found_non_splat = false

  offenses = when_conditions.reverse.map do |condition|
    found_non_splat ||= non_splat?(condition)

    next if non_splat?(condition)

    condition if found_non_splat
  end

  offenses.compact
end


  








  

    #when_branch_range(when_node)   (private)
  

  [ GitHub ]


  

  


# File 'lib/rubocop/cop/performance/case_when_splat.rb', line 126



def when_branch_range(when_node)
  next_branch = when_node.parent.when_branches[when_node.branch_index + 1]

  range_between(when_node.source_range.begin_pos, next_branch.source_range.begin_pos)
end