How can I create a function with a variable number of arguments?

Question

How can I create a function with a variable number of arguments in Rust?

Like this Java code:

void foo(String... args) {
    for (String arg : args) {
        System.out.println(arg);
    }
}

Answer 1

In general, you can't - Rust does not support variadic functions, except when interoperating with C code that uses varargs.

In this case, since all of your arguments are the same type, you can accept a slice:

fn foo(args: &[&str]) {
    for arg in args {
        println!("{}", arg);
    }
}

fn main() {
    foo(&["hello", "world", "I", "am", "arguments"]);
}

(Playground)

Beyond that, you can explicitly accept optional arguments:

fn foo(name: &str, age: Option<u8>) {
    match age {
        Some(age) => println!("{} is {}.", name, age),
        None      => println!("Who knows how old {} is?", name),
    }
}

fn main() {
    foo("Sally", Some(27));
    foo("Bill", None);
}

(Playground)

If you need to accept many arguments, optional or not, you can implement a builder:

struct Arguments<'a> {
    name: &'a str,
    age: Option<u8>,
}

impl<'a> Arguments<'a> {
    fn new(name: &'a str) -> Arguments<'a> {
        Arguments {
            name: name,
            age: None
        }
    }

    fn age(self, age: u8) -> Self {
        Arguments {
            age: Some(age),
            ..self
        }
    }
}

fn foo(arg: Arguments) {
    match arg.age {
        Some(age) => println!("{} is {}.", arg.name, age),
        None      => println!("Who knows how old {} is?", arg.name),
    }
}

fn main() {
    foo(Arguments::new("Sally").age(27));
    foo(Arguments::new("Bill"));
}

(Playground)