Attribute Macro

  编译退出码 0 []
  运行:
    [timed] add 返回了(耗时数量级 微秒以内)
    add = 5
    [timed] slow 返回了(耗时数量级 毫秒)
    slow = done
  展开后的 add:
    fn add(a: i32, b: i32) -> i32 {
        let __t = std::time::Instant::now();
        let __r = (|| { a + b })();
        {
            ::std::io::_print(format_args!("[timed] {0} 返回了(耗时数量级 {1})\n",
                    "add",
                    if __t.elapsed().as_millis() >= 1 {
                        "毫秒"
                    } else { "微秒以内" }));
        };
        __r
    }

  编译退出码 0
  运行:
    ("GET", "/users", "list_users")
    ("POST", "/users", "create_user")
    原函数仍可调用: users / created

  error: expected `,`
   --> src/main.rs:3:1
    |
  3 | #[route("GET")] fn a() {}
    | ^^^^^^^^^^^^^^^
    |
    = note: this error originates in the attribute macro `route` (in Nightly builds, run with -Z macro-backtrace for more info)
  error: expected string literal
   --> src/main.rs:4:9
    |
  4 | #[route(GET, "/x")] fn b() {}
    |         ^^^
  error: could not compile `app` (bin "app") due to 2 previous errors

  error[E0425]: cannot find function `gone` in this scope
     --> src/main.rs:4:28
      |
    4 | fn main() { println!("{}", gone()); }
      |                            ^^^^
      |

  error: expected `fn`
   --> src/main.rs:3:10
    |
  3 | #[timed] struct NotFn;
    |          ^^^^^^
  error: could not compile `app` (bin "app") due to 1 previous error