bench.rs

use criterion::{Criterion, criterion_group, criterion_main};
use std::hint::black_box;

fn format(cat: &str, name: &str) -> String {
    format!("{cat}.{name}")
}

fn push(cat: &str, name: &str) -> String {
    let mut s = String::new();
    s.push_str(cat);
    s.push('.');
    s.push_str(name);
    s
}

fn push_cap(cat: &str, name: &str) -> String {
    let mut s = String::with_capacity(1 + cat.len() + name.len());
    s.push_str(cat);
    s.push('.');
    s.push_str(name);
    s
}

fn push_array(items: &[&str]) -> String {
    let mut s = String::with_capacity(items.into_iter().map(|it| it.len()).sum());
    items.into_iter().for_each(|it| s.push_str(it));
    s
}

fn push_concat(items: &[&str]) -> String {
    items.concat()
}

fn criterion_benchmark(c: &mut Criterion) {
    let mut group = c.benchmark_group("concats");

    group.bench_function("format", |b| {
        b.iter(|| format(black_box("abc"), black_box("def")))
    });

    group.bench_function("concat", |b| {
        b.iter(|| push(black_box("abc"), black_box("def")))
    });

    group.bench_function("push_cap", |b| {
        b.iter(|| push_cap(black_box("abc"), black_box("def")))
    });

    group.bench_function("push_array", |b| {
        b.iter(|| push_array(black_box(&["abc", ".", "def"])))
    });

    group.bench_function("push_concat", |b| {
        b.iter(|| push_concat(black_box(&["abc", ".", "def"])))
    });

    group.finish();
}

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

Cargo.toml

[package]
name = "stringconcat-bench"
version = "0.1.0"
edition = "2024"

[dev-dependencies]
criterion = "0.8.2"

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

gistfile1.txt

     Running benches/bench.rs (target/release/deps/bench-86a27cae1c0ce77d)
concats/format          time:   [24.377 ns 24.509 ns 24.657 ns]
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild
concats/concat          time:   [15.779 ns 15.863 ns 15.947 ns]
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild
concats/push_cap        time:   [13.814 ns 13.850 ns 13.886 ns]
Found 3 outliers among 100 measurements (3.00%)
  3 (3.00%) high mild
concats/push_array      time:   [15.853 ns 15.924 ns 15.998 ns]
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
concats/push_concat     time:   [15.396 ns 15.461 ns 15.524 ns]
Found 10 outliers among 100 measurements (10.00%)
  4 (4.00%) low mild
  6 (6.00%) high mild