Parameters

Ferret supports value, reference, default, and variadic parameters.

Value Parameters

Value parameters follow Ferret’s ownership rules:

Copy for copyable types (for example i32, bool, and aggregates of copyable fields)
Move for non-copyable owned types (for example resource handles, #T, dynamic containers, and aggregates containing them)

fn add(a: i32, b: i32) -> i32 {
    return a + b;
}

import "std/fs";

fn close_file(f: fs::File) {
    f.Close();
}

fn main() {
    let file := fs::Create("out.txt") catch err {
        return;
    };

    close_file(file); // file is moved because fs::File is non-copyable
}

Reference Parameters

Use &T for read-only borrowing and &mut T for mutable borrowing.

fn sum(values: &[]i32) -> i32 {
    let total := 0;
    for v in values {
        total += v;
    }
    return total;
}

fn push_value(values: &mut []i32, v: i32) {
    append(values, v);
}

Use references when the callee should not take ownership:

&T for shared read-only access
&mut T for mutable access

Default Parameters

Parameters can declare defaults with =.

fn connect(host: str = "127.0.0.1", port: i32 = 6379) -> str {
    return host + ":" + port;
}

Rules:

Default parameters must be trailing.
A default expression cannot reference another parameter.

Variadic Parameters

Use ...T for variable argument lists.

fn sum(numbers: ...i32) -> i32 {
    let total := 0;
    for n in numbers {
        total += n;
    }
    return total;
}