[tarantool-patches] Re: [PATCH v2 2/2] lua: add key_def lua module

[Alexander Turenko]

> > >> Probably, we should reuse tuple_validate() for checking a tuple against
> > >> a key_def so as not to implement the same code again.
> > 
> > Unfortunately tuple_validate() is designed for format validation while we don't
> > have format here and I don't like create it for validation event in case of error.
> 
> Creating a format on each call to 'compare' is prohibitive from
> performance pov, you're right. However, we could attach a format to
> Lua's key_def object. This would also speed up comparisons, as tuples

So this module will not more be relatively simple layer that exposes
box/key_def into Lua and this again suggests me that the name key_def
maybe is not good choice.

> created for this format would have fieldmap.

Note: It will speed up comparisons only in case when a user give a lua
table as input, not when it give a tuple. However if a user give a tuple
it seems that it is in (s)he responsibility to think about the format.

And, while we're here, maybe it worth to provide a function like
box.tuple.new(), but with key_def instance as an argument to allow a
user to create tuples with necessary formats (to speed up comparisons
and other fields accesses)?

> However, what I don't like is that in case a tuple is created from a Lua
> table, you'll have to access all fields twice - on validation and
> comparison - which is costly without a fieldmap. One more argument for
> attaching a format to Lua's key_def object.

I think we can add *_unchecked() function variants like in
msgpack/msgpackffi if the peformance will be really a problem and
someone will request for them.