What does "not" do in the if statement?

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#1

Can you please explain to me what does " not " do in the if statement with an example?

Thanks!

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#2

“not” is self-explanatory: it checks if a condition isn’t truthy (anything other than nil or false)

local condition = false
if not condition then
   -- 'condition' is a falsy value, so this will pass
end

-- ^ this is the same as
if condition == false or condition == nil then
   --...
end

Yes

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#3

That’s what I thought, but I just wanted to make sure.

Also, take this code as an example

if not game.Workspace:FindFirstChild("Part") then

Does this check if the part doesn’t exist in the workspace?

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#4

if it doesnt find Part in workspace then it will count it as true

its the same as this

local part = workspace:FindFirstChild("Part")

if not part then
    print("Part is not in workspace")
else
    print("Part is in workspace")
end
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#5

Also, fun fact, using not 2 times is an easy way to convert anything into a bool value:

local function toBool(x: any): boolean
	return not not x
end

print(toBool(5)) --true
print(toBool(nil)) --false
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#6

yeah, this is also very helpful for toggling things that have bool values like GUI.Enabled or Frame.Visible (in some cases)

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#7

Simple toggle using not

local toggled = false
function toggle()
  toggled = not toggled
end
#8

The ‘not’ statement reverts an boolean;
If it’s true, it becomes false; If it’s false, becomes true.

Following this ‘false: true’ logic, when working with it on a if-statement, you’ll basically be checking if that condition is truthy, just like mentioned previously on this thread.

Examples of uses:

local is_true = true 

if not is_true then
     -- is not true
end

local boolean = false

-- Reverts it
boolean = not boolean
-- boolean is now true

And you can use it on ternary expressions too:

local can_afford = false

print(not can_afford and "You cannot buy this" or "You can buy this")
-- Following the logic of if statements, but on a single line

-- "and" on this expression acts like 'then', while "or" acts as else
-- Additional examples:

local can_afford = true
local is_selling = false


print(is_selling and (can_afford and "You can buy it, its on-sale" or "It's on-sale, but you can't buy it") or (can_afford and "It's not for sale, but you can afford it" or "It's not for sale and you can't afford it"))

----- is_selling: true
-- can_afford: "You can buy it, it's on sale"
-- not can_afford: "It's on sale, but you can't afford it"

----- is_selling: false
-- can_afford: "It's not for sale, but you can afford it"
-- not can_afford: "It's not for sale and you can't afford it"

However, it’s advisable to not be using ternary expressions on values that may be nil because it always ends up on a bug; In this case, you should be using the Luau addition if-then expression.

It works similarly to the if-then-end statement, but doesn’t require the ‘end’ part and is a expression.

Examples with the use of if-then expressions:

1:

local function GetCorrectText(can_afford)
     return if can_afford then "You can buy this" else "You can't buy this!"
end

print(GetCorrectText(true)) -- can_afford: true

2:

local can_afford = false

print(if can_afford then "You can buy this" or "You cannot buy this")

Additional informations:

Syntax - Luau.

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#9

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