Rust by Example: Functions

Functions are declared using the fn keyword. The returned value is specified using the -> arrow. The last expression in the function is the return value. Function names are in snake_case.
Run code Copy code 
fn main() {

Functions are declared using the fn keyword. This function takes two ints and returns an int.

 
    fn add(x: i32, y: i32) -> i32 {
        return x + y;
    }

    let result = add(1, 2);
    println!("Adding two numbers: {}", result);

A function with an implicit return, no semicolon is needed.

 
    fn subtract(x: i32, y: i32) -> i32 {
        x - y
    }

    let result = subtract(2, 1);
    println!("Subtracting two numbers: {}", result);

Functions can return multiple values, and this is done using tuples.

 
    fn swap(x: i32, y: i32) -> (i32, i32) {
        return (y, x);
    }

    let result = swap(1, 2);
    println!("Swapping two numbers: {} {}", result.0, result.1);

When functions don't return a value they return an empty tuple () known as a unit type.

 
    fn no_return() {}

    let result = no_return();
    println!("No return value: {:?}", result);
}

$ rustc functions.rs
$ ./functions
Adding two numbers: 3
Subtracting two numbers: 1
Swapping two numbers: 2 1
No return value: ()
Go to Index | Next: Closures