Stabilize Duration::span as-is?

[SimonSapin]

std::time currently contains:

impl Duration {
    /// Runs a closure, returning the duration of time it took to run the
    /// closure.
    #[unstable(feature = "duration_span",
               reason = "unsure if this is the right API or whether it should \
                         wait for a more general \"moment in time\" \
                         abstraction")]
    pub fn span<F>(f: F) -> Duration where F: FnOnce() {
        let start = SteadyTime::now();
        f();
        &SteadyTime::now() - &start
    }
}

I’d like to stabilize this method unchanged. Even if a "moment in time" abstraction exists, doing the let start = now(); do stuff; now() - start dance gets tedious very quickly and a closure-based Duration::span method would still be valuable.

[Stebalien]

I strongly disagree; IMO, this should really be a free-standing function (e.g. std::time::timeit). The time a function takes to run has nothing to do with time itself. This is kind of like adding a usize::count<I: Iterator>(i: I) -> usize function.

[SimonSapin]

That’s a good point, it probably should be moved. Though I’d still like to have one expression rather than three statements.

[gsingh93]

+1 for std::time::timeit.

[Stebalien]

Though I’d still like to have one expression rather than three statements.

Definitely.

[SimonSapin]

Closing in favor of rust-lang/rust#27799.