http://blog.sina.com.cn/s/blog_49bdd36d0100fdc1.html

lua 除了简单类型分配内存外，table只是传递引用，所以不能用简单的"="来copy两个表，并试图修改一个表中的值。
 
用以下方法实现table copy:
1.
function th_table_dup(ori_tab)
    if (type(ori_tab) ~= "table") then
        return nil;
    end
    local new_tab = {};
    for i,v in pairs(ori_tab) do
        local vtyp = type(v);
        if (vtyp == "table") then
            new_tab[i] = th_table_dup(v);
        elseif (vtyp == "thread") then
            -- TODO: dup or just point to?
            new_tab[i] = v;
         elseif (vtyp == "userdata") then
            -- TODO: dup or just point to?
            new_tab[i] = v;
        else
            new_tab[i] = v;
        end
    end
    return new_tab;
end
2. 
function deepcopy(object)
    local lookup_table = {}
    local function _copy(object)
        if type(object) ~= "table" then
            return object
        elseif lookup_table[object] then
            return lookup_table[object]
        end  -- if
        local new_table = {}
        lookup_table[object] = new_table
        for index, value in pairs(object) do
            new_table[_copy(index)] = _copy(value)
        end  -- for
        return setmetatable(new_table, getmetatable(object))
    end  -- function _copy
    return _copy(object)
end  -- function deepcopy
This function returns a deep copy of a given table. The function below also copies the metatable to the new table if there is one, so the behaviour of the copied table is the same as the original. But the 2 tables share the same metatable, you can avoid this by changing this 'getmetatable(object)' to '_copy( getmetatable(object) )'.