Re: Upcoming changes in Lua 5.4

["Soni \"They/Them\" L." <fakedme@...>]

On 2018-01-02 03:21 PM, Michael Nelson wrote:
> On 1/2/2018 6:18 AM, Roberto Ierusalimschy wrote:  ...
> > As already explained, you can use _ARG; but you can use also any other
> > name:
> >
> >    function foo (...=a) print(a.n) end
> >
> > _ARG is present both for compatibility (the above syntax will not even
> > compile in older versions) and for the main chunk (which does not have
> > a header to name this parameter).
>  I just love the new syntax. I assume select will continue to work as 
> usual, for old code and for use cases where it works better. The _ARG 
> name makes the parameter name for the main chunk consistent with Lua 
> _NAME practice, a good change. Any code broken by this last change 
> should be an easy fix: a simple search and replace.

Hmm... Would the following work (and, if so, would it be faster than the 
C API/built-in table.unpack)?

table.unpack = function(t, i, j)
  assert(type(t) == "table", "first arg to table.unpack must be table")
  i = i or 1
  j = j or rawlen(t)
  local oldn = rawget(t, "n")
  rawset(t, "n", j)
  local _ARG = t
  local function helper(t, oldn, ...)
    rawset(t, "n", oldn)
    return ...
  end
  return helper(t, oldn, select(i, ...)) -- I guess this select() is 
the limiting factor.
end

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