如何在 Rust 中实现后增量宏

Question

是否可以在 Rust 中实现后增量宏？

fn main() {
    let mut i = 0usize;
    let v = vec!(0,1,2,3,);
    println!("{}", post_inc!(i)); // 0
    println!("{}", post_inc!(i)); // 1
    // i = 3
}

Answer 1

是的！这很容易：

macro_rules! post_inc {
    ($i:ident) => { // the macro is callable with any identifier (eg. a variable)
        { // the macro evaluates to a block expression
            let old = $i; // save the old value
            $i += 1; // increment the argument
            old // the value of the block is `old`
        }
    };
}

fn main() {
    let mut i = 0usize;
    let v = vec![0, 1, 2, 3];
    println!("{}", post_inc!(i)); // 0
    println!("{}", post_inc!(i)); // 1
                                  // i = 3
}

（固定链接到操场）