Re: [PATCH] setmetatable({}) causes error

[Roberto Ierusalimschy <roberto@...>]

> Almost… ^,^  The easiest way to understand C functions from Lua is that
> they are always _vararg-only_ functions with no named parameters.  TNONE
> doesn't exist on the Lua side (it's an artifact of indexing beyond top
> of stack) but can be emulated by checking if the index is bigger than
> `select('#',...)`.
> 
> So you can actually treat C functions as a feature-limited subset of Lua
> functions, which is easy to understand.

Being vararg does not seem to be "feature-limited", quite the
opposite. We can think as if all functions in Lua were vararg. The
syntax

  function foo (a,b,c) 

can be considered basically a sugar for

  function foo (...)  local a,b,c = ...

and, therefore, a restriction over a more permissive vararg handling.

The main difference between Lua functions and C functions is that C
functions do not have this sugar available, and so it is easier (and
more efficient, and maybe more natural) for them to work directly on the
varargs. (A near equivalent to this sugar in C would be to start the C
function with a lua_settop.)

-- Roberto