Some experiments with new Lua table functions.

append-test.lua

require 'tablex'

local M = tonumber(arg[1]) or 10000
local N = tonumber(arg[2]) or 1000

local t_msg, t_start

function start_t (msg)
    t_msg = msg
    t_start = os.clock()
end

function end_t ()
    print(('%s: %6.1f sec'):format(t_msg,os.clock() - t_start))
end

local new = function(N) return {} end

if arg[3] then
    new = table.new
end

local function test_t_insert (N)
    local t_insert = table.insert
    local t = new(N)
    for i = 1,N do
        t_insert(t,i)
    end
end

local function test_t_append2 (N)
    local t_append = table.append
    local t = new(N)
    for i = 1,N,2 do
        t_append(t,i,i+1)
    end
end


local function test_t_plus (N)
    local t = new(N)
    for i = 1,N do
        t[#t + 1] = i
    end
end

local function append (t,v)
    t[#t+1] = v
end

local function test_t_plusfun (N)
    local t = new(N)
    for i = 1,N do
        append(t,v)
    end
end


local function test_t_set (N)
    local t = new(N)
    for i = 1,N do
        t[i] = i
    end
end


start_t 'table.insert'
for i = 1,M do
    test_t_insert(N)
end
end_t()


start_t 't[#t+1]=...'
for i = 1,M do
    test_t_plus(N)
end
end_t()

start_t 't[#t+1] as fun'
for i = 1,M do
    test_t_plusfun(N)
end
end_t()


start_t 't[i]=... loop i'
for i = 1,M do
    test_t_set(N)
end
end_t()

start_t 'table.append 2'
for i = 1,M do
    test_t_append2(N)
end
end_t()

tablex.c

#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

static int l_tnew (lua_State *L) {
    int narr = luaL_optint(L,1,0);   // initial array slots, default 0
    int nrec = luaL_optint(L,2,0);   // intial hash slots, default 0
    lua_createtable(L,narr,nrec);
    return 1;
}

static int l_tappend (lua_State *L) {
    int i,len = lua_objlen(L,1);
    int N = lua_gettop(L);
    for (i = 2; i <= N; i++) {
        lua_pushvalue(L,i);
        lua_rawseti(L,1,len+i-1);
    }
    return 0;
}

int luaopen_tablex(lua_State *L) {
    lua_getglobal(L,"table");
    lua_pushcfunction(L,l_tnew);
    lua_setfield(L,-2,"new");
    lua_pushcfunction(L,l_tappend);
    lua_setfield(L,-2,"append");
    return 0;
}

Drive-by pedantry: the arguments to table.new() in LuaJIT 2.1 aren't optional :)