Variable

(Redirected from Variables)

A variable is a name you can use to hold a value. In Lua, a variable can have any data type, such as a number or a string.

Assignment[edit]

Main article: Assignment

Assigning a value to a variable can be done using the = operator, like so:

x = 10
word = "Hello"

Variable x now has a value of the number 10, and word has a value of the string "Hello". If we print out these variables, we should see the value they have:

print(x)     --> 10
print(word)  --> Hello

A variable can be changed simply by assigning another value to it:

n = 12
print(n)    --> 12
 
n = 24
print(n)    --> 24

Even though n was assigned to a value of 12, its value was overwritten by the second assignment of 24.


You can also use a variable as a value when assigning.

n = 78
x = n
 
print(x)   --> 78

When x was assigned to n, it's value became the value of n.


Remember! A variable is always on the left side of the = while a value is on the right side.


Important! If you assign a variable to a property's value (e.g. Transparency), the variable will not change when the property does. To make a variable update with a property's value, you can include the code below in your scripts:

script.Parent.Changed:connect(function()
var = script.Parent.Name           -- Change the path and property name as appropriate to what you need
end)

Names[edit]

The name you give a variable can only contain letters (uppercase and lowercase), numbers, or an underscore ( _ ), this means that you shouldn't use space characters in the name of your variable. It must start with an underscore or a letter. It cannot be a keyword (one that is highlighted blue in the editor).

LETTERS = "ABC"          -- valid
x86 = 1978               -- valid
var_name = "variable"    -- valid
_ = "blank"              -- valid
 
if = 12                  -- NOT valid!
16th = "Lincoln"         -- NOT valid!

Remember! You must make sure when you call the variable later on in the script that you use the same uppercase and lowercase letters as you did when assigning it, e.g. using the example code above, Letters ~= "ABC" but LETTERS == "ABC".

Multiple Assignment[edit]

Lua allows you to assign more than one value to more than one variable.

a, b, c = 1, 2, 3
 
print(a, b, c)    --> 1 2 3

Each variable and each value is separated by a comma. Values to the right of the = are assigned to their corresponding variables to the left. The first variable is assigned to the first value, the second variable is assigned to the second value, and so on. The above example is the same as this. You can see how it saves a lot of space:

a = 1
b = 2
c = 3
 
print(a, b, c)    --> 1 2 3

Swapping[edit]

Multiple assignment is useful because it allows you to easily swap the values of two variables.

x, y = 8, 36
print(x, y)    --> 8 36
 
x, y = y, x
 
print(x, y)    --> 36 8

In this example, x is assigned to the original value of y, and y is assigned to the original value of x.


Variable Scopes[edit]

Main article: Scope
Every time a block is opened, a new scope is created. Variables in the outer scope are visible, while variables in the inner scope are not. Variables that aren't local are apart of the global scope (shown in blue), and are visible to all scopes, no matter where they were created.

Sometimes you may want to limit the access of one variable to another. You can do this by allowing a variable to be visible only to others in the same area. These areas are called scopes. In normal Lua, there are two scopes, known as global and local.

Each block of code has its own scope. Since blocks can be nested, each scope may have an outer scope and an inner scope.

  • The inner scope is a "child" of the current scope. The current scope cannot access variables in the inner scope.
  • The outer scope is a the "parent" of the current scope. The current scope has access to any variables in the outer scope.

Global Variables[edit]

See also: Global Functions

A global variable is a variable that is visible to all scopes of a script. (Not to be confused with adding variables to the "_G" or "shared" tables, which are shared amongst scripts.)

a = 1
if true then
    print(a)        --> 1
    if true then
        a = 2
        print(a)    --> 2
    end
    print(a)        --> 2
end
print(a)            --> 2

All variables will default to global, unless they are declared local (explained next).

Local Variables[edit]

A local variable is a variable that can only be accessed by other things in the same scope. A variable is made local by adding the keyword local before the variable. It is true that local variables are obtained faster than normal variables. This is because they are integrated into the current environment they were created in.

local word = "Hello"

A local variable is not visible to things in its outer scope.

if true then    -- a new block is created
    local b = 2
end
print(b)        --> nil

However, they are visible to things in its inner scope.

local b = 2
if true then
    print(b)    --> 2
end

If a variable has the same name as one in its outer scope, the outer scope's value is overwritten in the inner scope, but not the outer scope.

a = 1
if true then
    local a = 2
    print(a)      --> 2
end
print(a)          --> 1

Shared Variables[edit]

Shared variables are partially visible to the global scope, such that they can be accessed, but not changed.

In Roblox Lua, there is a third type of variable called a shared variable. Shared variables are variables that are visible to every script (that is, they are shared between them). Some examples of a shared variable include print, game, or Instance. A list of all shared variables can be found at the Function Dump.

Remember that there are some major differences between normal Lua and Roblox Lua.

  • In normal Lua, these variables are considered global variables, because they are completely visible in the global scope.
  • In Roblox Lua, these variables have been separated from the global scope because Roblox uses multiple scripts, each having their own environment.
  • In Roblox Lua, these variables cannot be modified for security reasons.

Practice[edit]

Exercise

Instructions

Using only two lines of code, perform the following actions:

  1. Assign the variables a,b, and c to the values 1, 2, and 3.
  2. Switch the values of a and c and change the value of b to 100.



Solution
Select
a, b, c = 1, 2, 3
a, b, c = c, 100, a