# File activesupport/lib/active_support/rescuable.rb, line 85
def handler_for_rescue(exception)
  # We go from right to left because pairs are pushed onto rescue_handlers
  # as rescue_from declarations are found.
  _, rescuer = self.class.rescue_handlers.reverse.detect do |klass_name, handler|
    # The purpose of allowing strings in rescue_from is to support the
    # declaration of handler associations for exception classes whose
    # definition is yet unknown.
    #
    # Since this loop needs the constants it would be inconsistent to
    # assume they should exist at this point. An early raised exception
    # could trigger some other handler and the array could include
    # precisely a string whose corresponding constant has not yet been
    # seen. This is why we are tolerant to unknown constants.
    #
    # Note that this tolerance only matters if the exception was given as
    # a string, otherwise a NameError will be raised by the interpreter
    # itself when rescue_from CONSTANT is executed.
    klass = self.class.const_get(klass_name) rescue nil
    klass ||= klass_name.constantize rescue nil
    exception.is_a?(klass) if klass
  end

  case rescuer
  when Symbol
    method(rescuer)
  when Proc
    if rescuer.arity == 0
      Proc.new { instance_exec(&rescuer) }
    else
      Proc.new { |_exception| instance_exec(_exception, &rescuer) }
    end
  end
end

# File activesupport/lib/active_support/rescuable.rb, line 78
def rescue_with_handler(exception)
  if handler = handler_for_rescue(exception)
    handler.arity != 0 ? handler.call(exception) : handler.call
    true # don't rely on the return value of the handler
  end
end