Feature Request: lazy once

[rokoroku]

Context

• node version: 6.9
• joi version: 10.6.1

const schema = Joi.lazy(() => Joi.any()).once()

Since fn for Joi.lazy(fn) should return joi schema, it's okay to be called once to avoid unnecessary overhead.

(+) My other need is describing lazily-loaded schema with Joi.describe().
If lazy.once() replace the schema as lazily loaded schema itself, we can now describe the lazy schema as well. (Could it be another feature request for Joi.describe()? )

[Marsup]

once could be a thing, but it's probably not a good idea for description as lazy is often used for cyclic or recursive patterns, so this would obviously result in endless descriptions.

[rokoroku]

@Marsup what about adding deep options to Joi.describe() ? Then it gives a chance to avoid cyclic schema

Come to think of it, describing lazy schema may harmful in many situations, and it's not likely to be widely used.