return - Rust
Description: API documentation for the Rust `return` keyword in crate `std`.
Keywords: rust, rustlang, rust-lang, return

# [−]Keyword return

Return a value from a function.

A `return` marks the end of an execution path in a function:

    fn foo() -> i32 {
        return 3;
    }
    assert_eq!(foo(), 3);

Run

`return` is not needed when the returned value is the last expression in the function. In this case the `;` is omitted:

    fn foo() -> i32 {
        3
    }
    assert_eq!(foo(), 3);

Run

`return` returns from the function immediately (an "early return"):

    use std::fs::File;
    use std::io::{Error, ErrorKind, Read, Result};

    fn main() -> Result<()> {
        let mut file = match File::open("foo.txt") {
            Ok(f) => f,
            Err(e) => return Err(e),
        };

        let mut contents = String::new();
        let size = match file.read_to_string(&mut contents) {
            Ok(s) => s,
            Err(e) => return Err(e),
        };

        if contents.contains("impossible!") {
            return Err(Error::new(ErrorKind::Other, "oh no!"));
        }

        if size > 9000 {
            return Err(Error::new(ErrorKind::Other, "over 9000!"));
        }

        assert_eq!(contents, "Hello, world!");
        Ok(())
    }

Run