【Rust 日报】2020-05-01 tco: 用过程宏实现的尾递归优化能力

  □ GitHub: https://github.com/RustCrypto/elliptic-curves/tree/master/p256
  □ crates.io: https://crates.io/crates/p256
  □ docs.rs: https://docs.rs/p256/

  □ GitHub: https://github.com/RustCrypto/elliptic-curves/tree/master/k256
  □ crates.io: https://crates.io/crates/k256
  □ docs.rs: https://docs.rs/k256/

#[tco::rewrite]
fn fac_with_acc(n: u128, acc: u128) -> u128 {
    if n > 1 {
        fac_with_acc(n - 1, acc * n)
    } else {
        acc
    }
}
优化后的代码为：fn fac_with_acc(n: u128, acc: u128) -> u128 {
    let mut n = n;
    let mut acc = acc;
    '__tco_loop: loop {
        return {
            if n > 1 {
                {
                    let __tco_0 = (n - 1, acc * n);
                    n = __tco_0.0;
                    acc = __tco_0.1;
                    continue '__tco_loop;
                }
            } else {
                acc
            }
        };
    }
}