Re: [Tarantool-patches] [PATCH v2 05/15] lua: don't raise a Lua error from luaT_tuple_new()

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

On 12.10.2020 12:37, Alexander Turenko wrote:
>>> Disallow creating a tuple from objects on the Lua stack (idx == 0) in
>>> luaT_tuple_new() for simplicity. There are no such usages in tarantool.
>>> The function is not exposed yet to the module API. This is only
>>> necessary in box.tuple.new(), which anyway raises Lua errors by its
>>> contract.
>>
>> 1. But why? The case of creating a tuple from values may be much faster,
>> when there is a lot of values not wrapped into a table. Table wrap is
>> costly.
>>
>> Could you just merge luaT_tuple_encode_values and luaT_tuple_encode_table
>> into one function, withuout splitting them?
> 
> I started with this variant, but then found that it'll require copying
> of all arguments before pcall() (at least if we must leave them on the
> stack after exiting from the function). Even if we'll decide to include
> a remark like 'the function pops all values in case of idx == 0', we'll
> need to put a function before the arguments and so we'll move all stack
> values. Anyway it looks lopsided: in one case arguments are popped, but
> in another they are kept on the stack.
> 
> I guess it would have a chance to be useful if it would allow to pass a
> range of lua stack indices. But not sure.

I created an issue for that: https://github.com/tarantool/tarantool/issues/5406
(At least it is related, and this place is not the only problematic one.)