Up until this point, if we wanted to assign a variable based on a condition, we would have to use an if-statement.

local a = 20
local animal = "whale"
local fruit = "apple"

local thing

if a > 10 then
    thing = animal
else
    thing = fruit
end

print(thing) -- Output: whale

A ternary operator is a feature in many other programming languages, like JavaScript. It is a short way to get a value based on a condition, and saves us from using an if-statement.

Officially, Lua does not have a ternary operator. But, by using and & or (see If-statements#and & or) we can simulate it.

local a = 20
local animal = "whale"
local fruit = "apple"

local thing = a > 10 and animal or fruit
print(thing) -- Output: whale

By doing this, we have achieved the same result as by using the if-statement.

Let's create some simple expressions to really understand what and and or do.

print("whale" and "apple" and "blue") -- Output: blue
print("whale" or "apple" or "blue") -- Output: whale
print( "whale" and "apple" or "blue") -- Output: apple

In the first expression, we start with the truthy value "whale". Because it is truthy, the and will continue to the next value. "apple" is also truthy, so again it will continue onto the next and. There we have the value "blue". There is not another and, so this is the value that this expression ends up with.

In the second expression, we again start with "whale". Because it is truthy, we are done. The or is for when the value on the left is falsy, which it's not. So "whale" is the value of this expression.

In the third example we again start with the value "whale". Truthy, so we continue with the and. Truthy, so we don't continue with the or. The value of this expression is "apple".

If you can keep up, let's use some parentheses to combine these expressions. Can you figure out the output of the code below?

local a = 20
local animal = "whale"
local fruit = "apple"

local thing = (a > 10 and 5 or 15) > 10 and animal or fruit
print(thing) -- Output: ???

local a = 20
local animal = nil
local fruit = "apple"
local thing = a > 10 and animal or fruit
print(thing) -- Output: apple