Problem

Since Javascript doesn't have a Tuple type, usually we represent tuples as "fixed"-size arrays.
Imagine that I want a sorted pair validation.

I could do something like:

const sortedPair = Joi.array().ordered([
    Joi.number().required(),
    Joi.number().min(Joi.ref('0')).required(),
]).required();

However, this doesn't work, because if I run:

Joi.validate([1, 2], sortedPair);

I get:

ValidationError: "value" at position 1 fails because ["1" references "0" which is not a number]

Interestingly, currently it's possible to achieve this behavior if:

1. I transform sortedPair into an object:

   const sortedPairObj = Joi.object().keys({
       low: Joi.number().required(),
       high: Joi.number().min(Joi.ref('low')).required(),
   }).required();

2. I wrap sortedPair into an object:

   const schema = Joi.object().keys({
     sortedPair: Joi.array()
       .ordered([
         Joi.number().required(),
         Joi.number()
           .min(Joi.ref('sortedPair.0'))
           .required(),
       ])
       .required(),
   });

As for 2., I also tried to do the following:

Joi.validate([1, 2], Joi.reach(schema, 'sortedPair'))

But once again I got an error:

ValidationError: "value" at position 1 fails because ["1" references "sortedPair.0" which is not a number]

Affected APIs

• .array()
• .ref()

Did I miss something?

If this is an actual issue, I thinks I might be able to work on a PR.