debug_time.rs

/// print the time that executing $timed took
/// but only when the log level is "debug".
/// The goal of this macro is to avoid doing useless
/// Instant::now in non Debug executions.
///
/// Examples:
/// ```
/// let sum = time!(
///     "summing",
///     2 + 2 // this is super hard
/// );
/// let mult = time!(3 * 4);
/// ```
macro_rules! time {
    ($timed: expr) => {{
        if log_enabled!(log::Level::Debug) {
            use std::time::Instant;
            let start = Instant::now();
            let value = $timed;
            debug!("{} took {:?}", stringify!($timed), start.elapsed());
            value
        } else {
            $timed
        }
    }};
    ($name: expr,  $timed: expr $(,)?) => {{
        if log_enabled!(log::Level::Debug) {
            use std::time::Instant;
            let start = Instant::now();
            let value = $timed;
            debug!("{} took {:?}", $name, start.elapsed());
            value
        } else {
            $timed
        }
    }};
    ($cat: expr, $name :expr,  $timed: expr $(,)?) => {{
        if log_enabled!(log::Level::Debug) {
            use std::time::Instant;
            let start = Instant::now();
            let value = $timed;
            debug!("{} on {:?} took {:?}", $cat, $name, start.elapsed());
            value
        } else {
            $timed
        }
    }};
}