msgpack.NULL is not nil!

[msiomkin]

https://www.tarantool.io/en/doc/2.2/book/box/data_model/#lua-vs-msgpack

This table maps msgpack.NULL to Lua nil. It's wrong. I think there should be cdata type.

[lenkis]

@msiomkin @kyukhin let's agree on this. what exactly do we want here?

[msiomkin]

As I already said I think it should be cdata. @kyukhin right?

[lenkis]

• to add explanations as suggested in Document box.NULL #561

[Totktonada]

The table shows msgpack and lua types and also has a colon that shows examples of a Lua value. msgpack nil type has the only value: 0xc0.

Let's verify Lua -> msgpack mapping:

tarantool> msgpack.encode(nil):hex()
---
- c0
...

tarantool> msgpack.encode(box.NULL):hex()
---
- c0
...

Let's verify msgpack -> Lua mapping:

tarantool> msgpack.decode('\xc0')
---
- null
- 2
...

tarantool> type(msgpack.decode('\xc0'))
---
- cdata
...

So, yep, box.NULL (msgpack.NULL) is symmetric here, but I don't think that it would be wrong to give nil value as an example.

Anyway, Mike asks to add a type (cdata) to the column with values examples. I don't understood a motivation of this request. It at least would not be consistent: some examples would be types, some would be values.

@msiomkin Am I missed something?