class RuboCop::Cop::Naming::MemoizedInstanceVariableName

This cop checks for memoized methods whose instance variable name does not match the method name.

This cop can be configured with the EnforcedStyleForLeadingUnderscores directive. It can be configured to allow for memoized instance variables prefixed with an underscore. Prefixing ivars with an underscore is a convention that is used to implicitly indicate that an ivar should not be set or referencd outside of the memoization method.

@example EnforcedStyleForLeadingUnderscores: disallowed (default)

# bad
# Method foo is memoized using an instance variable that is
# not `@foo`. This can cause confusion and bugs.
def foo
  @something ||= calculate_expensive_thing
end

# good
def _foo
  @foo ||= calculate_expensive_thing
end

# good
def foo
  @foo ||= calculate_expensive_thing
end

# good
def foo
  @foo ||= begin
    calculate_expensive_thing
  end
end

# good
def foo
  helper_variable = something_we_need_to_calculate_foo
  @foo ||= calculate_expensive_thing(helper_variable)
end

@example EnforcedStyleForLeadingUnderscores: required

# bad
def foo
  @something ||= calculate_expensive_thing
end

# bad
def foo
  @foo ||= calculate_expensive_thing
end

# good
def foo
  @_foo ||= calculate_expensive_thing
end

# good
def _foo
  @_foo ||= calculate_expensive_thing
end

@example EnforcedStyleForLeadingUnderscores :optional

# bad
def foo
  @something ||= calculate_expensive_thing
end

# good
def foo
  @foo ||= calculate_expensive_thing
end

# good
def foo
  @_foo ||= calculate_expensive_thing
end

# good
def _foo
  @_foo ||= calculate_expensive_thing
end

Constants

MSG
UNDERSCORE_REQUIRED

Private Class Methods

node_pattern() click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 95
def self.node_pattern
  memo_assign = '(or_asgn $(ivasgn _) _)'
  memoized_at_end_of_method = "(begin ... #{memo_assign})"
  instance_method =
    "(def $_ _ {#{memo_assign} #{memoized_at_end_of_method}})"
  class_method =
    "(defs self $_ _ {#{memo_assign} #{memoized_at_end_of_method}})"
  "{#{instance_method} #{class_method}}"
end

Public Instance Methods

on_def(node) click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 108
def on_def(node)
  (method_name, ivar_assign) = memoized?(node)
  return if matches?(method_name, ivar_assign)

  msg = format(
    message(ivar_assign.children.first.to_s),
    var: ivar_assign.children.first.to_s,
    suggested_var: suggested_var(method_name),
    method: method_name
  )
  add_offense(node, location: ivar_assign.source_range, message: msg)
end
Also aliased as: on_defs
on_defs(node)
Alias for: on_def

Private Instance Methods

matches?(method_name, ivar_assign) click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 128
def matches?(method_name, ivar_assign)
  return true if ivar_assign.nil? || method_name == :initialize

  method_name = method_name.to_s.delete('!?')
  variable = ivar_assign.children.first
  variable_name = variable.to_s.sub('@', '')

  variable_name_candidates(method_name).include?(variable_name)
end
message(variable) click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 138
def message(variable)
  variable_name = variable.to_s.sub('@', '')

  return UNDERSCORE_REQUIRED if style == :required &&
                                !variable_name.start_with?('_')

  MSG
end
style_parameter_name() click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 124
def style_parameter_name
  'EnforcedStyleForLeadingUnderscores'
end
suggested_var(method_name) click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 147
def suggested_var(method_name)
  suggestion = method_name.to_s.delete('!?')

  style == :required ? "_#{suggestion}" : suggestion
end
variable_name_candidates(method_name) click to toggle source
# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 153
def variable_name_candidates(method_name)
  no_underscore = method_name.sub(/\A_/, '')
  with_underscore = "_#{method_name}"
  case style
  when :required
    [with_underscore,
     method_name.start_with?('_') ? method_name : nil].compact
  when :disallowed
    [method_name, no_underscore]
  when :optional
    [method_name, with_underscore, no_underscore]
  else
    raise 'Unreachable'
  end
end