Module: Rigor::ValueSemantics::ClassMethods

Defined in:
lib/rigor/value_semantics.rb

Instance Method Summary collapse

Instance Method Details

#value_fields(*fields) ⇒ Object

Define ‘==` / `eql?` / `hash` over the given immutable fields.



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# File 'lib/rigor/value_semantics.rb', line 47

def value_fields(*fields)
  comparisons = fields.map { |f| "#{f} == other.#{f}" }
  guard = comparisons.empty? ? "" : " && #{comparisons.join(' && ')}"
  key = (["self.class"] + fields.map(&:to_s)).join(", ")

  # Codegen (not per-call reflection) so the generated `==` / `hash`
  # read fields directly and run at hand-written speed on the
  # inference hot path. For `value_fields :class_name, :type_args`
  # the emitted source is:
  #
  #   def ==(other)
  #     other.is_a?(self.class) && class_name == other.class_name && type_args == other.type_args
  #   end
  #   alias_method :eql?, :==
  #   def hash
  #     [self.class, class_name, type_args].hash
  #   end
  class_eval(<<~RUBY, __FILE__, __LINE__ + 1) # rubocop:disable Style/DocumentDynamicEvalDefinition
    def ==(other)
      other.is_a?(self.class)#{guard}
    end
    alias_method :eql?, :==

    def hash
      [#{key}].hash
    end
  RUBY
end