bench_starts_with.rs

#![feature(test)]

extern crate test;

#[cfg(test)]
mod tests {
    use super::*;
    use std::str;
    use test::Bencher;

    #[bench]
    fn bench_bytes_to_str(b: &mut Bencher) {
        let contents = "sample message";
        b.iter(|| contents.starts_with(str::from_utf8(&[b's', b'a', b'm']).unwrap()));
    }

    #[bench]
    fn bench_str_to_bytes(b: &mut Bencher) {
        let contents = "sample message";
        b.iter(|| contents.as_bytes().starts_with(&[b's', b'a', b'm']));
    }
}

rustc 1.27.0-nightly (bd40cbbe1 2018-04-14)

running 2 tests
test tests::bench_bytes_to_str ... bench:          14 ns/iter (+/- 7)
test tests::bench_str_to_bytes ... bench:           1 ns/iter (+/- 0)

test result: ok. 0 passed; 0 failed; 0 ignored; 2 measured; 0 filtered out

strをbytesに変換する方が14倍速い。(as_bytes()内部でやってるのはunsafeでのキャストのみなのでコストが小さい)