ruby-grape/grape · error · ArgumentError

with: #{with.class}, expected Symbol, String or Proc

Error message

with: #{with.class}, expected Symbol, String or Proc

What it means

The `with:` option of `rescue_from` must be a handler reference Grape can invoke: a Proc, a Symbol naming an endpoint method, or a String that is converted with to_sym. Any other class (Integer, Hash, Class, nil-replacement objects) raises ArgumentError with the offending class name, since Grape cannot dispatch it when an exception is raised at runtime.

Source

Thrown at lib/grape/dsl/request_response.rb:154

      def represent(model_class, with:)
        raise Grape::Exceptions::InvalidWithOptionForRepresent.new unless with.is_a?(Class)

        inheritable_setting.add_representation(model_class, with)
      end

      private

      def extract_handler(args, with:, block:)
        raise ArgumentError, 'both :with option and block cannot be passed' if block && with

        return args.pop if args.last.is_a?(Proc)
        return block if block
        return unless with

        case with
        when Proc, Symbol then with
        when String then with.to_sym
        else raise ArgumentError, "with: #{with.class}, expected Symbol, String or Proc"
        end
      end
    end
  end
end

View on GitHub (pinned to 22d7975629)

Solutions

1. Pass a Symbol naming a defined helper/instance method: `with: :render_error`.
2. Pass a Proc/lambda: `with: ->(e) { error!(e.message, 500) }` (String method names are also accepted and to_sym-ed).
3. If you need extra data, close over it in the Proc or define a dedicated method instead of passing a Hash.

Example fix

# before
rescue_from ArgumentError, with: { code: 400, msg: 'bad' } # raises with: Hash

# after
rescue_from ArgumentError, with: ->(e) { error!(e.message, 400) }

# or
rescue_from ArgumentError, with: :render_error
def render_error(e); error!({ code: 400, msg: e.message }, 400); end

def valid_with_option?(with) = with.is_a?(Proc) || with.is_a?(Symbol) || with.is_a?(String)

raise ArgumentError, 'with: must be Symbol, String, or Proc' unless valid_with_option?(my_with)

def handler_ref?(value) = value.is_a?(Proc) || value.is_a?(Symbol) || value.is_a?(String)

When it happens

Trigger: `rescue_from ArgumentError, with: 42` or `with: { message: 'err' }`. `with: SomeModule` (passing a class instead of a Proc). `with: 'render_error '`-style values are fine as Strings, but a frozen numeric/boolean option raises.

Common situations: Passing configuration hashes or objects intended for the handler body instead of a handler reference. Typos like `with: :render_errorrs`. Dynamically computing the handler and accidentally passing nil-replacement or non-callable values.

Related errors

• both :with option and block cannot be passed
• Status code must be Integer or Symbol.
• Argument must be a file path
• rescue_from #{meta_selector.inspect} does not accept additio
• Returning or throwing a Hash from a rescue handler is deprec

AI-assisted analysis of ruby-grape/grape@22d7975629 (2026-08-21). Data as JSON: /api/errors/f2eb58470d33f673. Report an issue: GitHub.