I have variable that contains a number. While Lua allows variables to be set to nil, the variable then becomes toxic - destroying all code in its path.
If a variable contains a nil, I want it converted to a zero.
local score;
score = gameResults.finalScore;
I want to ensure that score contains a number, so I try:
local score;
score = tonumber(gameResults.finalScore);
but that doesn't work. So I try:
local function ToNumberEx(v)
if (v == nil) then
return 0
else
return tonumber(v)
end
local score;
score = ToNumberEx(gameResults.finalScore);
but that doesn't work. So I try:
local function ToNumberEx(v)
if (v == nil) then
return 0
else
return tonumber(v)
end
local score;
score = ToNumberEx(gameResults.finalScore);
if (score == nil) then
score = 0
end
That works, but defeats the purpose of having a function.
What is wrong with the function? I'm sure there is a perfectly reasonable and logical explanation - except to anyone who is familiar with programming languages.
score = tonumber(gameResults.finalScore) or 0
If the argument is already a number or
a string convertible to a number, then
tonumber returns this number;
otherwise, it returns nil.
Your code was good, except you didn't take into account what happens when gameResult.finalScore can't be converted to a number, if it was " " or "stuff" or a table than tonumber would return nil. None of your checks could detect that kind of situation.
If you really want to enforce that this variable gameResults.finalScore has this behavior (set to zero when receives any value different from a number), than you should take a look at Lua metatables.
You could create a metatable for gameResults, and "overwrite" the "index" and "newindex" methods of the metatable, checking the value for the finalScore field, and thus enforcing it's value to be on the desired ranges.
Not the best solution, but depending on your case, could be a good defensive practice against some other "evil developer" on the team. :-)
www.lua.org/pil/13.html (I'm not currently allowed to post more than 1 link) PiL 1 can help too, if you are still using Lua 5.0 or you want a more deep understanding of the metatables concept.
Related
I was doing some anti metamethod hooks and I was curious on what metamethod is called in the code below between the parentheses
local test = "random string"
if (test == "random string") then --// What metamethod if any is being called here?
print("equals")
end
I've done some research and took a look at the __eq metamethod, but that is only called when comparing two tables which isn't what I'm tryna do.
If there isn't any metamethod being called then how would I protect the if condition?
-- Update --
What if I put every string inside of a table for example:
local _Table1 = {"Test1", "Test2"}
local _Table2 = {"Test1", "Test2"}
for Index, Value in next, _Table1 do
if Value == _Table2[Index] then
print("Tables Match!")
elseif Value ~= _Table2[Index]
print("Tables Don't Match!")
end
end
I'm not doing any string converting here, but I'm showing what I could try and do for a simple anti tamper.
The only operator in the parenthesized expression is ==. Thus the only metamethod in question is __eq. The Lua Reference Manual states the following on __eq:
__eq: the equal (==) operation. Behavior similar to the addition operation, except that Lua will try a metamethod only when the values being compared are either both tables or both full userdata and they are not primitively equal.
Your values are strings and thus no metamethod will be called - even if you were to modify the string metatable to alter __eq.
Strings in Lua are always interned, so this comparison will always run in constant time. Since it is a primitive comparison, it can't possibly throw an error. No metamethod is called.
There is nothing to protect from: No possible performance issue / DoS vulnerability, no possible fancy side effects or code execution, no possible error.
(Highly theoretically: If a debug hook running every n instructions is registered, it might fire as the comparison is executed. You can hardly "protect" against a debug hook though.)
But it makes sense, for example a check against the Length.
A check against the Content seems also possible but need more lines.
And i like one liner in Lua Standalone to show...
> _VERSION
Lua 5.4
> eqtab = setmetatable({"Test1", "Test2"}, {__eq = function(left, right) print('SIMON SAYS:') return(#left == #right) end})
> eqtab == {1}
SIMON SAYS:
false
> eqtab == {}
SIMON SAYS:
false
> eqtab == {"Test1", "Test2"}
SIMON SAYS:
true
> eqtab == {1, 2}
SIMON SAYS:
true
I am attempting to make a Lua script for an online community I am a part of, I am having a problem when I attempt to search through a table array I believe. It doesn't detect the results I want.
The way it is supposed to work is that when someone types /gps [streetname] it will search the table at the top, detect the matching streetname & the coordinates and then set a waypoint to that relevant position.
At the moment it works when there is just one entry in the table, but when I put more, it will provide the error message for any non-matching streets & then the waypoint set message for the matching streets. I've Googled and don't appear to be able to find anything to help.
Any help would be appreciated.
waypoint = {
{404.08, -920.23, 'sinnerstreet', 'Sinner Street'},
{360.85, -956.46, 'atleestreet', 'Atlee Street'},
{500.48, -956.80, 'littlebighornavenue', 'Little Bighorn Avenue'},
}
RegisterCommand('gps', function(source, args, rawCommand)
for k,v in pairs(waypoint) do
x, y, streetname, displayname = table.unpack(v)
results = ""
if args[1] == nil then
if IsWaypointActive() then
SetWaypointOff()
TriggerEvent('chatMessage', '^1^*GPS Navigation: ^r^7Your GPS system has been reset.')
return end
elseif args[2] == nil and args[3] == nil then
results = args[1]
elseif args[2] ~= nil and args[3] == nil then
results = args[1] .. args[2]
else
results = args[1] .. args[2] .. args[3]
end
results = string.lower(results) -- This convertes the args into lower case
end
-- This locates the streetname and sets a waypoint to it for the player
if string.find(streetname, results) then
SetNewWaypoint(x, y)
TriggerEvent('chatMessage', '^1^*GPS Navigation: ^r^7Your waypoint to ^1' .. displayname .. '^r^7 has been set.')
else
TriggerEvent('chatMessage', '^1^*GPS Navigation: ^r^7There has been an error with your street name, please try again.')
end
end)
TriggerEvent('chat:addSuggestion', '/gps', 'This creates a waypoint to your designated street. ^*USE: /gps [streetname]')
To be honest, your code makes little to no sense, and it's probably because you're not using all the nice stuff Lua has to offer.
{404.08, -920.23, 'sinnerstreet', 'Sinner Street'},
You're storing redundant data there. The third value is really just the fourth one with spaces removed and all lowercase.
'sinnerstreet' == ('Sinner Street'):gsub("[^%l]", ""):lower()
In english: take "Sinner Street", globally (meaning in the entire string) substitute everything that is not a lowercase (%l) letter with nothing (""), then make the result of that lowercase. What you get is "sinnerstreet".
x, y, streetname, displayname = table.unpack(v)
Using globals there, that's not good. Globals are the devil. Don't use them.
Then, a few lines further down:
SetNewWaypoint(x, y)
Think about it for a moment. You set x and y in each iteration of your for loop. After the loop is done, they always contain the coordinates of the last waypoint you iterated over. I doubt that's what you want. Use local; it forces you to think what you want the scope of your variables to be, which will help you spot this kind of problem.
elseif args[2] ~= nil and args[3] == nil then
results = args[1] .. args[2]
Unless you specifically want to limit it to 3 arguments, which I doubt, you can also use table.concat to concatenate all the values in a sequence (read: array)
results = string.lower( table.concat(args) )
The thing that puzzles me is why you do this in a loop. For every waypoint, you set result to the same value, which is all the arguments concatenated and converted to lower case.
now what though? You check if result (what the user searched for) contains streetname, which, as we have previously found out, contains the name of the last waypoint in the list.
Using tables for searching
Lua has tables, one of if not the most powerful general-purpose data structure in programming.
local map = {}
for _,waypoint in ipairs(waypoints) do
map[waypoint[3]:lower()] = waypoint
end
This will get you something that looks about like this:
local map = {
sinnerstreet = {404.08, -920.23, 'sinnerstreet', 'Sinner Street'},
atleestreet = {360.85, -956.46, 'atleestreet', 'Atlee Street'},
littlebighornavenue ={500.48, -956.80, 'littlebighornavenue', 'Little Bighorn Avenue'},
}
and if you want to know if a street exists, you can just do this:
if map['atleestreet'] then
print(map.atleestreet[4])
end
if treats everything that isn't false or nil as truthy, so you can just write `map['atleestreet'] in the condition
my_table['text'] can be written as my_table.text
Looking up string indices in a table is pretty fast because of how it's implemented.
Conclusion
Try thinking your code through. If necessary, go through it line by line, writing down what values the variables hold in each moment. If you've been at it for a while, get some rest first or do something else for a while.
Then set your variables to local wherever possible (read: everywhere), figure out what needs to be inside and outside the loop and try again.
Remarks
Instead of if something == nil you can just write if not something, and if something ~= nil just if something
Apologies
Sorry for the long wall of text and using spaces inside brackets, but I wanted things to be specially easy to understand.
Ive been coding for a mod Im making for a game but I ran into an issue with tables not returning values when the key is entered:
for k, v in pairs(self.math) do
print(self.exce[1])
print(self.exce[k])
print(k)
if self.exce[k] ~= nil then
self.math[k] = nil
end
end
This is the specific part of the script that is breaking. When I run these in the game it returns:
[lua]: true
[lua]: nil
[lua]: 1
Which means is basically saying that 1 is not equal to 1.
The function I used to store my data is
function filterExceptions.server_onException( self, id )
if self.exce[id] == nil then
self.exce[id] = true
self.network:sendToClients( "client_onList", id )
else
self.exce[id] = true
self.network:sendToClients( "client_offList", id )
end
end
In this code the self is a table made by the game you can acces and get game data from or store it in and the id comes from a function I made to get the players id. This id in this case is a 1 (I printed it multiple times).I know that every part of this code is working except for the code in the first block, and escpecialy the part where it tries to do self.exce[k]. Ive tried a lot like going trough every variable in self.exce to see if it was in there and then do stuff, but it still wouldn't work. Its very annoying how lua thinks that k ~= 1 while it definitely is, ive even used similar code in a part that is working.
So what is wrong about this code that its not printing the self.exce[k] while self.exce[1] does work? Dont worry about the creation of the table and stuff, cuz that is already happening whenever it is needed, else it would have given errors about that too.
Putting together a couple different comments and your code here, it looks like the index value of the array in some particular iteration of the "for in pairs" loop (or perhaps all of them, but I'll touch on that in a minute) is a string instead of an integer.
To summarize if you don't want to read the entire thing, "for k, v in pairs" loops will iterate through an entire array, setting k to the index of the value v. It appears your "for in pairs" loop is attempting to iterate through a value of nil where k is a string instead of an integer. You may also want to look into using ipairs instead of pairs in your for loop.
The value of someArray[1]is different than the value of someArray["1"].
The index [1] is a completely different index than the index ["1"] for any given array.
A simple fix would be to use
ind = tonumber(k)
print(self.exce[ind])
This converts the string k to a number type. Be aware this may throw an error if k is a non-numerical string. If the array has any values where the index is a non-numerical string, you may get an error. As the other answer suggests, converting the index k to a string instead of an integer would work as well, and would not throw errors if you used a non-numerical value for your indices.
My guess as to why this is happening would be that the function that you're using to store your data to an array, filterExceptions.server_onException( self, id ), is being passed a string instead of an integer, which would result in the k value being set to a string in that particular iteration of the "for in pairs" loop.
To help better understand this, here's a bit of example code:
a = {true, false, false}
a[1] = true
a["1"] = true
print("Raw for in pairs loop")
for k, v in pairs (a) do
print(type(k)..k)
end
print("For in pairs converting k to a number")
for k, v in pairs (a) do
ind = tonumber(k)
print(type(ind)..ind)
end
print("For in ipairs")
--which I'm not sure I completely understand but
--it seems to skip over any iteration where k is not a number
for k, v in ipairs(a) do
print(type(k)..k)
end
This code produces the following output:
Raw for in pairs loop
number1
number2
number3
string1
For in pairs converting k to a number
number1
number2
number3
number1
For in ipairs
number1
number2
number3
EDIT: Not sure what's going on in the self.math table so I can't comment on that.
EDIT2: I'd also refer you to the following link: lua: iterate through all pairs in table
The top answer there should help understand the difference between pairs and ipairs, if you don't already. You may want to use ipairs to prevent values of k where v == nil from being iterated through with pairs. pairs will iterate through every key/value pair, whereas ipairs will iterate through integer keys starting at 1 and going until it hits a nil value.
EDIT3: I'm sorry this is such a long answer...I just wanted to be thorough.
It apears converting the id to a string fixes this, tough im still confused as to why this same code worked on another block and not this one.
function filterExceptions.server_onException( self, id )
local id2 = tostring(id)
if self.exce[id2] == nil then
self.exce[id2] = true
self.network:sendToClients( "client_onList", id )
else
self.exce[id2] = true
self.network:sendToClients( "client_offList", id )
end
end
I have a function in lua, which is given 2 vectors, return the lambda multiplier of first vector to second one, here is my code
function Math.vectorLambda( v1,v2 )
local v1Length,v2Length=math.sqrt(v1.x^2+v1.y^2),math.sqrt(v2.x^2+v2.y^2)
if v1Length==0 then
return nil
else
local dotProduct=v1.x*v2.x+v1.y*v2.y
print(dotProduct,v1Length,v2Length,math.abs(dotProduct)==(v1Length*v2Length))
if math.abs(dotProduct)==(v1Length*v2Length) then
if v1.x~=0 then
return v2.x/v1.x
else
return v2.y/v1.y
end
else
return nil
end
end
end
However, if
--this is what I get from terminal and I believe that it does not display the whole number--
v1={0.51449575542753,-0.85749292571254}
v2={-10,16.666666666667}
the output is
-19.436506316151 1 19.436506316151 false
which is saying the absolute value of dotProduct and v1Length*v2Length are not the same...
What is the reason for above, rather than I am blind? :(
BTW, the function is not stable..with exactly the same vectors, the function might has the same output except math.abs(dotProduct)==(v1Length*v2Length) gives true and hence return correct answer rather than nil, why?
Floats are tricky. You most likely have differences on the smaller decimal places (I don't know for sure, since I get true here). Try printing the numbers with a bigger precision, using a function like:
function prec_print(v, prec)
local format = '%.' .. prec .. 'f'
print(string.format(format, value))
end
In any case, you should almost never use == to compare floating point equality. For floats, it's quite easy to get false for simple things like a+b-b==a. What you should probably do is to check whether de difference of the two values is less than some threshold:
function almost_equal(float1, float2, threshold)
return math.abs(float1 - float2) <= threshold
end
But it's actually trickier than that (if, say, float1 and float2 are too far apart). Anyway, this read is mandatory for anyone working with floats: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
Cheers!
I came across a problem while writing some code up for a game. It seems I can't use variables in statements like;
local Username = "Cranavvo"
game.Players.Username:BreakJoints() -- Kills the player
And the output is telling me "No such user as 'Username'" which should be "Cranavvo".
From Lua PiL on tables
To represent records, you use the field name as an index. Lua supports
this representation by providing a.name as syntactic sugar for
a["name"].
A common mistake for beginners is to confuse a.x with a[x]. The first
form represents a["x"], that is, a table indexed by the string "x".
Therefore, when you try:
game.Players.Username:BreakJoints()
Lua interprets it as:
game["Players"]["Username"]:BreakJoints()
which ofcourse is wrong. If you want to use varying name as index for a table, use them like this:
local foo = "Cranavvo"
game.Players[foo]:BreakJoints()
But to be mentioned is that the Player class do not have a BreakJoints method, you have to get the character model with help of the .Character attribute like this:
local foo = "Cranavvo"
game.Players[foo].Character:BreakJoints()
Also to be mentioned is that if the player with that name does not exist the code will break, and also that the character can be null, in which case it also breaks. Thus you need to add some error handling. Like this:
local foo = "Cranavvo"
local Player = game.Players:findFirstChild(foo)
if Player ~= nil and Player.Character ~= nil then
Player.Character:BreakJoints()
end
The correct way to do this in roblox is this:
local Username = "Cranavvo"
local p = game.Players:FindFirstChild(Username)
if(p ~= nil) then
if(p.Character ~= nil) then
p.Character:BreakJoints()
end
end
Double check if the user really exists at the time your code gets executed.
Also it should be:
game.Players.Username:BreakJoints()
EDIT:
I misread what you wanted to do:
in
...Players.Username
lua interprets Username as a named index and does not use the Username variable declared beforehand.
If you want to access an array variable with a dynamic name you can do it like this:
game.Players[Username]:BreakJoints()
additionally in roblox you could just use the following:
game.Players:GetPlayerByID(userId):BreakJoints()
Variables are very confusing in Lua sometimes.
For example, there are global and local variables.
Local variables are variables that can be forgotten/erased after the operation ends: local x = 2
Global variables are variables that stay within the game/application unforgotten, this is good with high scores and other neat things. x = 2 (Notice there isn't a "local" statement)