Class: RuboCop::Cop::Style::YodaExpression

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::AutoCorrector, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/style/yoda_expression.rb


Forbids Yoda expressions, i.e. binary operations (using *, +, &, |, and ^ operators) where the order of expression is reversed, eg. 1 + x. This cop complements Style/YodaCondition cop, which has a similar purpose.

This cop is disabled by default to respect user intentions such as:

config.server_port = 9000 + ENV["TEST_ENV_NUMBER"].to_i


SupportedOperators: ['*', '+', '&', '|', '^'] (default)

# bad
10 * y
1 + x
1 & z
1 | x
1 ^ x

# good
y * 10
x + 1
z & 1
x | 1
x ^ 1
60 * 24

Cop Safety Information:

  • This cop is unsafe because binary operators can be defined differently on different classes, and are not guaranteed to have the same result if reversed.

Constant Summary

::RuboCop::Cop::Base - Inherited


Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,

Returns if class supports autocorrect.


Override if your cop should be called repeatedly for multiple investigations Between calls to on_new_investigation and on_investigation_end, the result of processed_source will remain constant.

Class Method Summary

::RuboCop::Cop::Base - Inherited


List of cops that should not try to autocorrect at the same time as this cop.



.callbacks_needed, .cop_name, .department,

Returns an url to view this cops documentation online.


Call for abstract Cop classes.


Override and return the Force class(es) you need to join.


Returns true if the cop name or the cop namespace matches any of the given names.


Register a version requirement for the given gem name.


::RuboCop::ExcludeLimit - Extended


Sets up a configuration option to have an exclude limit tracked.


Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::Base - Inherited


Adds an offense that has no particular location.


Adds an offense on the specified range (or node with an expression) Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense.


Called before any investigation.


Configuration Helpers.

#cop_name, #excluded_file?,

This method should be overridden when a cop’s behavior depends on state that lives outside of these locations:


Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.


Alias for Base#cop_name.


Called after all on_…​


Called before all on_…​


Called instead of all on_…​


There should be very limited reasons for a Cop to do it’s own parsing.


Called between investigations.

#relevant_file?, #target_rails_version, #target_ruby_version, #annotate, #apply_correction, #attempt_correction,

Reserved for Cop::Cop.


Called to complete an investigation.

#correct, #current_corrector,

Reserved for Commissioner:

#current_offenses, #currently_disabled_lines, #custom_severity, #default_severity, #disable_uncorrectable, #enabled_line?, #file_name_matches_any?, #find_message, #find_severity, #range_for_original, #range_from_node_or_range,

Actually private methods.


::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

This class inherits a constructor from RuboCop::Cop::Base

Instance Method Details

#constant_portion?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 73

def constant_portion?(node)
  node.numeric_type? || node.const_type?

#offended_ancestor?(node) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 81

def offended_ancestor?(node)
  node.each_ancestor(:send).any? { |ancestor| @offended_nodes&.include?(ancestor) }

#offended_nodes (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 85

def offended_nodes
  @offended_nodes ||= Set.new.compare_by_identity


[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 47

def on_new_investigation
  @offended_nodes = nil


[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 51

def on_send(node)
  return unless supported_operators.include?(node.method_name.to_s)

  lhs = node.receiver
  rhs = node.first_argument
  return unless yoda_expression_constant?(lhs, rhs)
  return if offended_ancestor?(node)

  message = format(MSG, source: rhs.source)
  add_offense(node, message: message) do |corrector|
    corrector.swap(lhs, rhs)


#supported_operators (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 77

def supported_operators

#yoda_expression_constant?(lhs, rhs) ⇒ Boolean (private)

[ GitHub ]

# File 'lib/rubocop/cop/style/yoda_expression.rb', line 69

def yoda_expression_constant?(lhs, rhs)
  constant_portion?(lhs) && !constant_portion?(rhs)