I need to get the variable a function's return value is assigned to.
function example()
end
variable = 3 --just for example
variable = example() --I need the value of variable(in this case 3) passed as an argument to example()
Please read the Lua reference on how to call and define functions.
https://www.lua.org/manual/5.3/manual.html#3.4.10
https://www.lua.org/manual/5.3/manual.html#3.4.11
You can simply do this:
function fancyFunction(val)
return val
end
local val = 3
val = fancyFunction(val)
of course this minimum example does not make much sense. You should of course have another return value than your argument. Otherwise you don't have to call the function in the first place.
(Quite hard to understand what you're trying to do.) Could you possibly be referring to object oriented programming? If so, then you need something like this:
--setup
t = {}
function t:set(v) self.value = v end --assign value to 'variable'
function t:get() return self.value end
--use
t:set(3)
print(t:get())
Related
In WebhookScript, I can store a function in a variable with:
sub = function(a, b) {
return a - b
}
I'd like to store a function in a Global Variable so that I can use it in multiple Custom Actions. But if I've saved the above function as $sub$ then
sub2 = var('$sub$')
subX = sub(1,2)
causes an error:
Trying to invoke a non-function 'string' # line...
And
function subX(a,b){
var('$sub$')
}
when sub only contains return a - b, doesn't work either.
Obviously I need to convert the string to a function but I'm not sure whether that's possible.
I know this is a bit of an obscure language but if anyone knows how this can be done in similar languages like JavaScript and PHP, I'm happy to test out any guesses...
The solution here is to remove the function section and just enter the script, which inherits the execution scope so if my global variable $script$ is:
return 'hello ' + a
Then I can execute the function with:
a = 'world'
value = exec(var('$script$'))
echo(value)
(credit to Webhook.Site's support team for explaining this)
Ok here goes...
I have been experimenting on various examples of declaring functions with "self" in the parameters.
I don't have full understanding of this which is what I'm trying to fully understand. I'm a complete beginner, but I am compelled to grasp this fully.
The 2 examples below return the same results, although in example 2, if I don't declare "self = {}" within the function, I need to place "self" (or the ":") in the function parameters for it to work. Is this the whole deal with "self"?
Are there other implications when using "self"?
Example 1
function Character.new(x)
self = {}
self.name = x
return self.name
end
a = Character
b = Character
hobbit = a.new ("Frodo")
dragon = b.new ("Smaug")
print (hobbit)
print (dragon)
Example 2
Character = {}
function Character:new(x)
self.name = x
return self.name
end
a = Character
b = Character
hobbit = a:new ("Frodo")
dragon = b:new ("Smaug")
print (hobbit)
print (dragon)
;^)
Zalokin
You're using global variables when you should be creating instances.
Try these lines instead, they may help you understand:
-- example 1
print (hobbit)
print(self.name)
print (dragon)
print(self.name)
and
-- example 2
print (hobbit)
print(Character.name)
print (dragon)
print(Character.name)
: lets you access the table which includes the function from within the function without an explicit (first argument) pass. It can be used both when defining and calling a function.
The example below contains a table t. The table has 3 functions (a,b and c) and a string entry under the key greeting.
All the function/method calls print the same string "hello user".
Notice how you can still call a method (a function which has its container table as the first argument) the same way as a normal function, but you have to explicitly pass the table as the first argument.
The self argument can be called what ever you want and you can still call the function with a : as long as you use the correct argument name inside the function (not self in this case). The function c serves as an example of that.
It is basically just syntax sugar.
local t = {}
t.greeting = "hello"
function t:a(name)
print(self.greeting, name)
end
function t.b(self, name)
print(self.greeting, name)
end
function t.c(myself, name)
print(myself.greeting, name)
end
t.a(t, "user")
t:a("user")
t.b(t, "user")
t:b("user")
t.c(t, "user")
t:c("user")
function [TC]=Translate(T0,Base)
end
I know that Translate is a function and T0 and Base his parameter but what is [TC]?
Octave (and matlab) have a rather unique way of returning variables from functions. Instead of defining explicitly what to return from the function using a return keyword, they define from the outset which variables will be returned when the function exits, and octave simply looks for those variables by name at the time the function exits, and returns their values, whatever they may be by that point.
Your function may return nothing:
function returnsNothing();
disp('hello, I return nothing');
end
or it may return one output:
function Out = returnsOne(x)
Out = x+5
disp('This function will return the value of Out');
end
or it may return more than one outputs:
function [Out1, Out2] = returnsTwo(x)
Out1 = x+5;
Out2 = x+10;
end
You would call the last function from the octave terminal (or script) like this:
[a,b] = returnsTwo(5); % this will make a = 10 and b = 15
I've been learning lua and can't seem to make a simple implementation of this binary tree work...
function createTree(tree, max)
if max > 0 then
tree = {data = max, left = {}, right = {}}
createTree(tree.left, max - 1)
createTree(tree.right, max - 1)
end
end
function printTree(tree)
if tree then
print(tree.data)
printTree(tree.left)
printTree(tree.right)
end
end
tree = {}
createTree(tree, 3)
printTree(tree)
the program just returns nil after execution. I've searched around the web to understand how argument passing works in lua (if it is by reference or by value) and found out that some types are passed by reference (like tables and functions) while others by value. Still, I made the global variable "tree" a table before passing it to the "createTree" function, and I even initialized "left" and "right" to be empty tables inside of "createTree" for the same purpose. What am I doing wrong?
It is probably necessary to initialize not by a new table, but only to set its values.
function createTree(tree, max)
if max > 0 then
tree.data = max
tree.left = {}
tree.right = {}
createTree(tree.left, max - 1)
createTree(tree.right, max - 1)
end
end
in Lua, arguments are passed by value. Assigning to an argument does not change the original variable.
Try this:
function createTree(max)
if max == 0 then
return nil
else
return {data = max, left = createTree(max-1), right = createTree(max-1)}
end
end
It is safe to think that for the most of the cases lua passes arguments by value. But for any object other than a number (numbers aren't objects actually), the "value" is actually a pointer to the said object.
When you do something like a={1,2,3} or b="asda" the values on the right are allocated somewhere dynamically, and a and b only get addresses of those. Thus, when you pass a to the function fun(a), the pointer is copied to a new variable inside function, but the a itself is unaffected:
function fun(p)
--p stores address of the same object, but `p` is not `a`
p[1]=3--by using the address you can
p[4]=1--alter the contents of the object
p[2]=nil--this will be seen outside
q={}
p={}--here you assign address of another object to the pointer
p=q--(here too)
end
Functions are also represented by pointers to them, you can use debug library to tinker with function object (change upvalues for example), this may affect how function executes, but, once again, you can not change where external references are pointing.
Strings are immutable objects, you can pass them around, there is a library that does stuff to them, but all the functions in that library return new string. So once, again external variable b from b="asda" would not be affected if you tried to do something with "asda" string inside the function.
As a beginner in Lua, I am sorry if the answer on this is easy.
I was trying to call a function within a code, yet after 2 hours of searching I couldn't find the wanted results. (Maybe I use the wrong search query's?)
Example code
function Test123 ()
SayTest = True
if SayTest = True then
-- This Is where I want to call the function name Test123,
-- yet I can't seem to succeed in this since it is just
-- starting a new function
SystemNotice ( role, function)
end
end
This should be the result:
function Test123 ()
SayTest = True
if SayTest = True then
SystemNotice ( role, 'Test123')
end
end
If anyone can help me out, I would be thankful. If I am still being unclear, just tell me and I will try to describe it better. My excuses for my limited English.
In Lua functions are actually values. That means they do not really have a name, you can only assign them to a variable or table field, but since the value itself has no concept of its name, you can't retrieve it.
That said, with the debug library, you can do this:
function getfname()
return debug.traceback("", 2):match("in function '(.-)'");
end
function bar()
print(getfname())
end
bar(); -- prints bar
foo = bar;
foo() -- prints foo
knerf = {rab = bar};
knerf.rab() -- prints rab
Note that this only works with the default Lua error handler or one that returns the same or very similar output, however you can obviously modify the pattern to suit what you need.
Read this: I would not advise this solution for performance-intensive tasks. Both string matching and the traceback are not really suited for this. Also, obviously the debug library must be enabled so you can actually use the traceback function.
Your function declaration lacks anend.
function Test123 ()
end
Read the functions chapter from the Lua manual. Just for the record, your if will also need an end.
This is a construct that just goes against the Lua philosophy that functions are first class citizens:
a function is just another value, and as such it has no name.
A variable can be assigned a value, thus binding a function to a name.
But that name can change. or a function can have multiple names. Which one to pick?
A better solution would be creating an anonymous function with an upvalue (a closure) instead:
function genTest(name)
return function()
SayTest = true
if SayTest == true then
print ( 'role', name)
end
end
end
Test123 = genTest('Test123')
Test123()
foobar = Test123
foobar()
This creates a function with a bound local variable name (see PiL 6.1 ).