The Question Mark `?` Operator in Rust

// Unified `Error` enum#[derive(Debug)]enum Error {    ParseIntError(std::num::ParseIntError),    ParseFloatError(std::num::ParseFloatError),}impl std::fmt::Display for Error {    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {        match self {            Self::ParseIntError(e) => write!(f, "ParseIntError: {}", e.to_string()),            Self::ParseFloatError(e) => write!(f, "ParseFloatError: {}", e.to_string()),        }    }}impl std::error::Error for Error {}// Convert `std::num::ParseIntError` to `Error`impl From<std::num::ParseIntError> for Error {    fn from(err: std::num::ParseIntError) -> Self {        Self::ParseIntError(err)    }}// Convert `std::num::ParseFloatError` to `Error`impl From<std::num::ParseFloatError> for Error {    fn from(err: std::num::ParseFloatError) -> Self {        Self::ParseFloatError(err)    }}fn main() -> Result<(), Error> {    // Parse an integer and unwrap it, or throw `Error::ParseIntError`    let _: i32 = "123".parse()?;    let _: i32 = "not_an_integer".parse()?;    // Parse a float and unwrap it, or throw `Error::ParseFloatError`    let _: f64 = "not_a_number".parse()?;    Ok(())}

fn get_first_char_of_second_word(phrase: &str) -> Option<char> {    // Return `None` if the phrase consist of a single word    phrase.split(" ").skip(1).next()?.chars().next()}fn main() {    assert_eq!(get_first_char_of_second_word("Hello World"), Some('W'));    assert_eq!(get_first_char_of_second_word("Hello?"), None);}