Small starts_with benchmark

bench.rs

/* Put this into Cargo.toml and the below code under benches/bench.rs:

[package]
name = "startbench"
version = "0.1.0"
edition = "2021"

[[bench]]
name = "bench"
harness = false

[dependencies]
criterion = "0.5.1"

*/

use criterion::{black_box, criterion_group, criterion_main, BenchmarkId, Criterion};

pub fn benchmark(c: &mut Criterion) {
    let chars = ['a', 'ö', '\u{1F609}'];
    let mut char_group = c.benchmark_group("char");
    for (i, t) in chars.iter().enumerate() {
        char_group.bench_with_input(BenchmarkId::from_parameter(i), t, |b, &t| {
            b.iter(|| black_box("whoa!".starts_with(black_box(t))))
        });
    }
    char_group.finish();

    let mut str_group = c.benchmark_group("&str");
    for (i, t) in chars.into_iter().enumerate() {
        let s = t.to_string();
        str_group.bench_with_input(BenchmarkId::from_parameter(i), &s[..], |b, s| {
            b.iter(|| black_box("whoa!".starts_with(black_box(s))))
        });
    }
    str_group.finish();
}

criterion_group!(benches, benchmark);
criterion_main!(benches);