Class: RuboCop::Cop::Lint::FloatComparison

Inherits:
Base
  • Object
show all
Defined in:
lib/rubocop/cop/lint/float_comparison.rb

Overview

Checks for the presence of precise comparison of floating point numbers.

Floating point values are inherently inaccurate, and comparing them for exact equality is almost never the desired semantics. Comparison via the ‘==/!=` operators checks floating-point value representation to be exactly the same, which is very unlikely if you perform any arithmetic operations involving precision loss.

Examples:

# bad
x == 0.1
x != 0.1

# bad
case value
when 1.0
  foo
when 2.0
  bar
end

# good - using BigDecimal
x.to_d == 0.1.to_d

# good - comparing against zero
x == 0.0
x != 0.0

# good
(x - 0.1).abs < Float::EPSILON

# good
tolerance = 0.0001
(x - 0.1).abs < tolerance

# good - comparing against nil
Float(x, exception: false) == nil

# good - using epsilon comparison in case expression
case
when (value - 1.0).abs < Float::EPSILON
  foo
when (value - 2.0).abs < Float::EPSILON
  bar
end

# Or some other epsilon based type of comparison:
# https://www.embeddeduse.com/2019/08/26/qt-compare-two-floats/

Constant Summary collapse

MSG_EQUALITY = 
'Avoid equality comparisons of floats as they are unreliable.'
MSG_INEQUALITY = 
'Avoid inequality comparisons of floats as they are unreliable.'
MSG_CASE = 
'Avoid float literal comparisons in case statements as they are unreliable.'
EQUALITY_METHODS = 
%i[== != eql? equal?].freeze
FLOAT_RETURNING_METHODS = 
%i[to_f Float fdiv].freeze
FLOAT_INSTANCE_METHODS = 
%i[@- abs magnitude modulo next_float prev_float quo].to_set.freeze
RESTRICT_ON_SEND = 
EQUALITY_METHODS

Instance Attribute Summary

Attributes inherited from Base

#config, #processed_source

Instance Method Summary collapse

Methods inherited from Base

#active_support_extensions_enabled?, #add_global_offense, #add_offense, #always_autocorrect?, autocorrect_incompatible_with, badge, #begin_investigation, #callbacks_needed, callbacks_needed, #config_to_allow_offenses, #config_to_allow_offenses=, #contextual_autocorrect?, #cop_config, #cop_name, cop_name, department, documentation_url, exclude_from_registry, #excluded_file?, #external_dependency_checksum, inherited, #initialize, #inspect, joining_forces, lint?, match?, #message, #offenses, #on_investigation_end, #on_new_investigation, #on_other_file, #parse, #parser_engine, #ready, #relevant_file?, requires_gem, #string_literals_frozen_by_default?, support_autocorrect?, support_multiple_source?, #target_gem_version, #target_rails_version, #target_ruby_version

Methods included from ExcludeLimit

#exclude_limit

Methods included from AutocorrectLogic

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #autocorrect_with_disable_uncorrectable?, #correctable?, #disable_uncorrectable?, #safe_autocorrect?

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

silence_warnings

Constructor Details

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

Instance Method Details

#on_case(node) ⇒ Object 



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# File 'lib/rubocop/cop/lint/float_comparison.rb', line 78

def on_case(node)
  node.when_branches.each do |when_branch|
    when_branch.each_condition do |condition|
      next if !float?(condition) || literal_safe?(condition)

      add_offense(condition, message: MSG_CASE)
    end
  end
end

#on_send(node) ⇒ Object Also known as: on_csend 



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# File 'lib/rubocop/cop/lint/float_comparison.rb', line 65

def on_send(node)
  return unless node.arguments.one?

  lhs = node.receiver
  rhs = node.first_argument

  return if literal_safe?(lhs) || literal_safe?(rhs)

  message = node.method?(:!=) ? MSG_INEQUALITY : MSG_EQUALITY
  add_offense(node, message: message) if float?(lhs) || float?(rhs)
end