【Rust】标准库-问号

环境

• Rust 1.56.1
• VSCode 1.61.2

概念

参考：https://doc.rust-lang.org/stable/rust-by-example/std/result/question_mark.html

示例

main.rs

mod checked {
    #[derive(Debug)]
    enum MathError {
        DivisionByZero,
        NonPositiveLogarithm,
        NegativeSquareRoot,
    }

    type MathResult = Result<f64, MathError>;

    fn div(x: f64, y: f64) -> MathResult {
        if y == 0.0 {
            Err(MathError::DivisionByZero)
        } else {
            Ok(x / y)
        }
    }

    fn sqrt(x: f64) -> MathResult {
        if x < 0.0 {
            Err(MathError::NegativeSquareRoot)
        } else {
            Ok(x.sqrt())
        }
    }

    fn ln(x: f64) -> MathResult {
        if x <= 0.0 {
            Err(MathError::NonPositiveLogarithm)
        } else {
            Ok(x.ln())
        }
    }

    fn op_(x: f64, y: f64) -> MathResult {
        let ratio = div(x, y)?;
        let ln = ln(ratio)?;
        sqrt(ln)
    }

    pub fn op(x: f64, y: f64) {
        match op_(x, y) {
            Err(why) => panic!(
                "{}",
                match why {
                    MathError::NonPositiveLogarithm => "logarithm of non-positive number",
                    MathError::DivisionByZero => "division by zero",
                    MathError::NegativeSquareRoot => "square root of negative number",
                }
            ),
            Ok(value) => println!("{}", value),
        }
    }
}

fn main() {
    checked::op(1.0, 10.0);
}

总结

了解了 Rust 中问号的使用方式，可以解开 Result。

附录