Ternary Operator

HolySwordExcaIiber · July 28, 2021, 2:20am

Guys I forgot how to do it what is the ternary operator for saying " If this is true then do this else do this" but you can use it with something like “true and 0 or 5” or something?

I have this Body Velocity function and I just wanna know how the operator works so I can basically say instead of 3.5 I want to say if Combo < 4 then It’s 3.5 otherwise It’s 45, thanks.

local BodyVelocity = Library.Functions.BodyVelocity(EnemyCharacter.HumanoidRootPart,Player.Character.HumanoidRootPart.CFrame.LookVector * 3.5,Vector3.new(100000,0,100000),0.1)

HolySwordExcaIiber · July 28, 2021, 2:23am

Before Someone responds with “well you can just do if combo <4 then variable = 3.5 else variable = 45 end” I know I can do that clearly but I want to know how the operator works since this is a commonly needed thing.

steven4547466 · July 28, 2021, 2:26am

local a = x and y or z

if x is truthy, the value will be y, else z

Updating old post:
Luau now supports built in ternary! local a = if x then y else z is the syntax. Learn why and more here:

Luau Recap: October 2021

if-then-else expression

In addition to supporting standard if statements , Luau adds support for if expressions . Syntactically, if-then-else expressions look very similar to if statements. However instead of conditionally executing blocks of code, if expressions conditionally evaluate expressions and return the value produced as a result. Also, unlike if statements, if expressions do not terminate with the end keyword.

Here is a simple example of an if-then-else expression:
local maxValue = if a > b then a else b
if-then-else expressions may occur in any place a regular expression is used. The if-then-else expression must match if <expr> then <expr> else <expr> ; it can also contain an arbitrary number of elseif clauses, like if <expr> then <expr> elseif <expr> then <expr> else <expr> . Note that in either case, else is mandatory.

Here’s is an example demonstrating elseif :
local sign = if x < 0 then -1 elseif x > 0 then 1 else 0
Note: In Luau, the if-then-else expression is preferred vs the standard Lua idiom of writing a and b or c (which roughly simulates a ternary operator). However, the Lua idiom may return an unexpected result if b evaluates to false. The if-then-else expression will behave as expected in all situations.

HolySwordExcaIiber · July 28, 2021, 2:28am

so I can put something like

HumanoidRootPart.CFrame.LookVector * combo < 4 and 3.5 or 45

steven4547466 · July 28, 2021, 2:32am

Should work, but look vector is a vector, so checking if it’s less than will probably throw an error along the lines of attempt to compare Vector3 < number

AstrealDev · July 28, 2021, 2:36am

I think this is what you want:

HumanoidRootPart.CFrame.LookVector * (combo < 4 and 3.5 or 45)

HolySwordExcaIiber · July 28, 2021, 2:42am

wait so putting parenthesis will stop it from throwing a error? Do parenthesis in lua when doing equations and suff ensure it runs what inside and gets the result before comparing code like the vector 3 and result of the ternary operator?

steven4547466 · July 28, 2021, 2:43am

Parentheses change the order of execution. So (combo < 4 and 3.5 or 45) will be resolved and then the result multiplied to the vector.

HolySwordExcaIiber · July 28, 2021, 2:45am

oh didn’t know that thankyou so that should stop it from erroring when I test it thanks.

0Luke_Skywalker0 · July 28, 2021, 2:50am

One thing to note is that due to the logic of the short circuit evaluation, the second expression (right after the and) can not be nil or false for it to work properly, or it will always go to the third one. But an easy fix is to just negate the first expression

Existile · January 8, 2022, 3:17pm

Good note, but it would just be easier to use if-then-else expressions as they get rid of this problem instead of using and-or as shown in the post up above