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)