Function Declaration

Functions are declared with the func keyword.

func Greet() {
    Print("Hello!");
}

Parameters and Return Types

Each parameter is written name: Type; the return type follows ->. A function without -> returns nothing. Multiple values can be returned as a tuple:

func Add(a: int32, b: int32) -> int32 {
    return a + b;
}

func Clamp(value: float64, min: float64, max: float64) -> float64 {
    if value < min { return min; }
    if value > max { return max; }
    return value;
}

func MinMax(arr: Slice<uint64>) -> (uint64, uint64) {
    var min = arr[0];
    var max = arr[0];
    for val in arr {
        if val < min { min = val; }
        if val > max { max = val; }
    }
    return (min, max);
}

By convention function names use PascalCase (see Identifiers).

Mutable Parameters

Like a let binding, a parameter is immutable by default — the body may read it but not reassign it. Prefix the parameter with var to make it a mutable local the body can reassign:

func Countdown(var n: int32) {
    while n > 0 {
        Print(n);
        n -= 1;        // OK — n is a var parameter
    }
}

The var governs only the parameter binding inside the function. Arguments are passed by value, so reassigning a var parameter never affects the caller's value. To modify the caller's value, take a pointer parameter instead.

Default Arguments

A parameter may declare a default value with =. A caller can then omit that argument and the default is used in its place. Parameters with defaults come after those without:

func Connect(host: Slice<char8>, port: uint16 = 443) {
    // Code here
}

Connect("example.com");        // port defaults to 443
Connect("example.com", 8080);  // port given explicitly

A default may be a compile-time intrinsic such as #source.file or #source.line, which the compiler substitutes at each call site — the pattern the standard library uses to capture a caller's location.

See Also

• Variadic Functions — accepting any number of arguments
• Generic Functions — parameterising over types
• Tuples — returning several values at once