Functions are reusable pieces of code that can do calculations. Pretty much like functions in any other programming language.

Parameter types need to be specified explicitly, return type is automatically deduced.

fn min(s32 a, s32 b) {
    if (a > b)
        return b;
        return a;

std::print(min(100, 200)); // 100

Parameter packs 1.14.0

To allow passing an unlimited number of parameters to functions, parameter packs can be used.

fn print_sequence(auto first, auto ... rest) {
    std::print("{}", first);

    if (std::sizeof_pack(rest) > 0)

print_sequence(1, 2, 3, 4, 5, 6);

Parameter packs can exclusively be used as arguments to other functions. Using them automatically expands them acting as if the contained values get passed to the other function individually.

The above function will print out all passed values in sequence by printing the first parameter and then removing it by not passing it on to the function during the next run.

Default parameters 1.17.0

Default parameters can be used to set a default value for parameters, if they weren provided when the functon got called.

fn print_numbers(u32 a, u32 b, u32 c = 3, u32 d = 4) {
    std::print("{} {} {} {}", a, b, c, d);

print_numbers(1, 2);            // Prints 1 2 3 4
print_numbers(8, 9, 10, 11);    // Prints 8 9 10 11

Reference parameters 1.23.0

Reference parameters can be used to avoid unnecessarily copying lots of data around and are helpful when needing to pass custom types that do not have a fixed layout to a function. Instead of copying the given parameter value onto the function’s heap, a reference to the existing pattern is instead used.

struct MyString {
    char value[while(std::mem::read_unsigned($, 1) != 0xFF)];

fn print_my_string(ref MyString myString) {


Variables can be declared in a similar fashion as outside of functions but they will be put onto the function’s stack instead of being highlighted.

fn get_value() {
    u32 value;
    u8 x = 1234;

    value = x * 2;

    return value;

Custom types may also be used inside of functions 1.19.0

union FloatConverter {
    u32 integer;
    float floatingPoint;

fn interpret_as_float(u32 integer) {
    FloatConverter converter;

    converter.integer = integer;
    return converter.floatingPoint;

_ variable 1.19.0

Variables named _ are treated as no-ops. Creating a variable with this name will cause its definition and assignment to it be discarded.

Control statements


If, Else-If and Else statements work the same as in most other C-like languages. When the condition inside a if head evaluates to true, the code in its body is executed. If it evaluates to false, the optional else block is executed.

Curly braces are optional and only required if more than one statement is present in the body.

if (x > 5) {
    // Execute when x is greater than 5
} else if (x == 2) {
    // Execute only when x is equals to 2
} else {
    // Execute otherwise


While loops work similarly to if statements. As long as the condition in the head evaluates to true, the body will continuously be executed.

while (check()) {
    // Keeps on executing as long as the check() function returns true

For-Statement 1.12.0

For loops are another kind of loop similar to the while loop. Its head consists of three blocks separated by commas. The first block is a variable declaration which will only be available inside the current for loop. The second block is a condition that will continuously be checked. The body is executed as long as this condition evaluates to true. The third block is a variable assignment which will be executed after all statements in the body have run.

// Declare a variable called i available only inside the for
for (u8 i = 0, i < 10, i = i + 1) {
    // Keeps on executing as long as i is less than 10

    // At the end, increment i by 1

Loop control flow statements 1.13.0

Inside of loops, the break and continue keyword may be used to to control the execution flow inside the loop.

When a break statement is reached, the loop is terminated immediately and code flow continues after the loop. When a continue statement is reached, the current iteration is terminated immediately and code flow continues at the start of the loop again, checking the condition again.

Return statements

In order to return a value from a function, the return keyword is used.

The return type of the function will automatically be determined by the value returned.

fn get_value() {
    return 1234;

std::print("{}", get_value()); // 1234