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()
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# 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)
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# 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
Private Instance Methods
matches?(method_name, ivar_assign)
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# 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)
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# 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()
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# File lib/rubocop/cop/naming/memoized_instance_variable_name.rb, line 124 def style_parameter_name 'EnforcedStyleForLeadingUnderscores' end
suggested_var(method_name)
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# 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)
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# 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