Luau and C# Comparison

Roblox uses the Luau programming language. The following code samples and tables indicate some of the differences between syntaxes for C# and Luau.

Line Endings

You don't need semicolons in Luau, but they don't break the syntax.

Reserved Keywords

The following table has Luau's reserved keywords mapped to their C# equivalent. Note it doesn't show all C# keywords.

Comments

Comments in Luau
-- Single line comment

--[[ Resulting output:
	Block comment
--]]

Comments in C#
// Single line comment

/*
	Block comment
*/

Strings

Strings in Luau
-- Multi-line string
local multiLineString = [[This is a string that,
when printed, appears
on multiple lines]]

-- Concatenation
local s1 = "This is a string "
local s2 = "made with two parts."
local endString = s1 .. s2

Strings in C#
// Multi-line string
string multiLineString1 = "This is a string that,\nwhen printed, appears\n on multiple lines.";

string multiLineString2 = @"This is a string that,
when printed, appears
on multiple lines";

// Concatenation
string s1 = "This is a string ";
string s2 = "made with two parts.";
string endString = s1 + s2;

Tables

To learn more about tables in Luau, see Tables.

Dictionary Tables

You can use tables in Luau as dictionaries just like in C#.

Dictionary Tables in Luau
local dictionary = {
	val1 = "this",
	val2 = "is"
}

print(dictionary.val1)  -- Outputs 'this'
print(dictionary["val1"])  -- Outputs 'this'

dictionary.val1 = nil  -- Removes 'val1' from table
dictionary["val3"] = "a dictionary"  -- Overwrites 'val3' or sets new key-value pair

Dictionary Tables in C#
Dictionary dictionary = new Dictionary()
{
	{ "val1", "this" },
	{ "val2", "is" }
};

Console.WriteLine(dictionary["val1"]);  // Outputs 'this'
dictionary.Remove("val1");  // Removes 'val1' from dictionary

dictionary["val3"] = "a dictionary";  // Overwrites 'val3' or sets new key-value pair
dictionary.Add("val3", "a dictionary");  // Creates a new key-value pair

Numerically-Indexed Tables

You can use tables in Luau as arrays just like in C#. Indices start at 1 in Luau and 0 in C#.

Numerically-Indexed Tables in Luau
local npcAttributes = {"strong", "intelligent"}

print(npcAttributes[1])  -- Outputs 'strong'
print(#npcAttributes)  -- Outputs the size of the list

-- Append to the list
table.insert(npcAttributes, "humble")
-- Another way...
npcAttributes[#npcAttributes+1] = "humble"

-- Insert at the beginning of the list
table.insert(npcAttributes, 1, "brave")

-- Remove item at a given index
table.remove(npcAttributes, 3)

Numerically-Indexed Tables in C#
List npcAttributes = new List{"strong", "intelligent"};

Console.WriteLine(npcAttributes[0]);  // Outputs 'strong'
Console.WriteLine(npcAttributes.Count);  // Outputs the size of the list

// Append to the list
npcAttributes.Add("humble");
// Another way...
npcAttributes.Insert(npcAttributes.Count, "humble");

// Insert at the beginning of the list
npcAttributes.Insert(0, "brave");

// Remove item at a given index
npcAttributes.Remove(2);

Operators

Conditional Operators

Arithmetic Operators

Variables

In Luau, variables don't specify their type when you declare them. Luau variables don't have access modifiers, although you may prefix "private" variables with an underscore for readability.

Variables in Luau
local stringVariable = "value"

-- "Public" declaration
local variableName

-- "Private" declaration - parsed the same way
local _variableName

Variables in C#
string stringVariable = "value";

// Public declaration
public string variableName

// Private declaration
string variableName;

Scope

In Luau, you can write variables and logic in a tighter scope than their function or class by nesting the logic within do and end keywords, similar to curly brackets {} in C#. For more details, see Scope.

Scoping in Luau
local outerVar = 'Outer scope text'

do
    -- Modify 'outerVar'
    outerVar = 'Inner scope modified text'
    -- Introduce a local variable
    local innerVar = 'Inner scope text'
    print('1: ' .. outerVar)    -- prints "1: Inner scope modified text"
    print('2: ' .. innerVar)    -- prints "2: Inner scope text"
end

print('3: ' .. outerVar)        -- prints "3: "Inner scope modified text"
-- Attempting to print 'innerVar' here would fail

Scoping in C#
var outerVar = "Outer scope text";

{
	// Modify 'outerVar'
	outerVar = "Inner scope modified text";
	// Introduce a local variable
	var innerVar = "Inner scope text";
	Console.WriteLine("1: " + outerVar);    // prints "1: Inner scope modified text"
	Console.WriteLine("2: " + innerVar);    // prints "2: Inner scope text"
}

Console.WriteLine("3: " + outerVar);		// prints "3: "Inner scope modified text"
// Attempting to print 'innerVar' here would fail

Conditional Statements

Conditional Statements in Luau
-- One condition
if boolExpression then
	doSomething()
end

-- Multiple conditions
if not boolExpression then
	doSomething()
elseif otherBoolExpression then
	doSomething()
else
	doSomething()
end

Conditional Statements in C#
// One condition
if (boolExpression) {
	doSomething();
}


// Multiple conditions
if (!boolExpression) {
	doSomething();
}
else if (otherBoolExpression) {
	doSomething();
}
else {
	doSomething();
}

Conditional Operator

Conditional Operator in Luau
local max = if x > y then x else y

Conditional Operator in C#
int max = (x > y) ? x : y;

Loops

To learn more about loops in Luau, see Control Structures.

While and Repeat Loops

While and Repeat Loops in Luau
while boolExpression do
	doSomething()
end

repeat
	doSomething()
until not boolExpression

While and Repeat Loops in C#
while (boolExpression) {
	doSomething();
}

do {
	doSomething();
} while (boolExpression)

For Loops

Generic For Loops in Luau
-- Forward loop
for i = 1, 10 do
	doSomething()
end

-- Reverse loop
for i = 10, 1, -1 do
	doSomething()
end

Generic For Loops in C#
// Forward loop
for (int i = 1; i <= 10; i++) {
	doSomething();
}

// Reverse loop
for (int i = 10; i >= 1; i--) {
	doSomething();
}

For Loops Over Tables in Luau
local abcList = {"a", "b", "c"}

for i, v in ipairs(abcList) do
	print(v)
end

local abcDictionary = { a=1, b=2, c=3 }

for k, v in pairs(abcDictionary) do
	print(k, v)
end

For Loops Over Lists in C#
List<string> abcList = new List<string>{"a", "b", "c"};

foreach (string v in abcList) {
	Console.WriteLine(v);
}

Dictionary<string, int> abcDictionary = new Dictionary<string, int>
{ {"a", 1}, {"b", 2}, {"c", 3} };


foreach (KeyValuePair<string, int> entry in abcDictionary) {
	Console.WriteLine(entry.Key + " " + entry.Value);
}

Luau also supports generalized iteration, which further simplifies working with tables.

Functions

To learn more about functions in Luau, see Functions.

Generic Functions

Generic Functions in Luau
-- Generic function
local function increment(number)
	return number + 1
end

Generic Functions in C#
// Generic function
int increment(int number) {
	return number + 1;
}

Variable Argument Number

Variable Argument Number in Luau
-- Variable argument number
local function variableArguments(...)
	print(...)
end

Variable Argument Number in C#
// Variable argument number
void variableArguments(params string[] inventoryItems) {
	for (item in inventoryItems) {
		Console.WriteLine(item);
	}
}

Named Arguments

Named Arguments in Luau
-- Named arguments
local function namedArguments(args)
	return args.name .. "'s birthday: " .. args.dob
end

namedArguments{name="Bob", dob="4/1/2000"}

Named Arguments in C#
// Named arguments
string namedArguments(string name, string dob) {
	return name + "'s birthday: " + dob;
}

namedArguments(name: "Bob", dob: "4/1/2000");

Try-Catch Structures

Try/Catch Structures in Luau
local function fireWeapon()
	if not weaponEquipped then
		error("No weapon equipped!")
	end
	-- Proceed...
end

local success, errorMessage = pcall(fireWeapon)
if not success then
	print(errorMessage)
end

Try/Catch Structures in C#
void fireWeapon() {
	if (!weaponEquipped) {
		// Use a user-defined exception
		throw new InvalidWeaponException("No weapon equipped!");
	}
	// Proceed...
}

try {
	fireWeapon();
} catch (InvalidWeaponException ex) {
	// An error was raised
}