Function meta_displace

library/LuaWrapper.cpp:628–677

* Method: displace for DF object references. * * Returns: a reference with the same type, but modified address */

 * Returns: a reference with the same type, but modified address
 */
static int meta_displace(lua_State *state)
{
    int argc = lua_gettop(state);

    bool has_step = (argc >= 3);
    if ((argc < 2 || argc > 3) ||
        !lua_isnumber(state, 2) ||
        (has_step && !lua_isnumber(state, 3)))
    {
        luaL_error(state, "Usage: object:_displace(index[,step]) or df._displace(object,...)");
    }

    int index = lua_tointeger(state, 2);
    int step = has_step ? lua_tointeger(state, 3) : 1;

    // Two special cases: nil and lightuserdata for NULL and void*
    if (lua_isnil(state, 1))
    {
        lua_pushnil(state);
        return 1;
    }

    if (lua_islightuserdata(state, 1))
    {
        if (!has_step)
            luaL_error(state, "Step is mandatory in _displace of void*");

        auto ptr = (uint8_t*)lua_touserdata(state, 1);
        lua_pushlightuserdata(state, ptr + index*step);
        return 1;
    }

    const type_identity *id = get_object_identity(state, 1, "df._displace()");

    if (!has_step)
        step = id->byte_size();

    if (index == 0 || step == 0)
    {
        lua_pushvalue(state, 1);
    }
    else
    {
        auto ptr = (uint8_t*)get_object_ref(state, 1);
        lua_getmetatable(state, 1);
        push_object_ref(state, ptr + index*step);
    }

    return 1;
}

/**
 * Method: allocation for DF object references.