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

Inherits:
Base
  • Object
show all
Extended by:
AutoCorrector
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.

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.'
ARRAY_MSG = 
'Pass the contents of array literals directly to `when` conditions.'

Instance Method Summary collapse

Instance Method Details

#on_case(case_node) ⇒ Object 



66
67
68
69
70
71
72
73
74
75
76
77
78
79
 
# 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