[dev-dependencies]
criterion = { version = "0.5", features = ["html_reports"] }

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

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

fn benchmark(c: &mut Criterion) {
    c.bench_function("fib", |b| {
        b.iter(|| fibonacci(black_box(20)))
    });
}

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

cargo install flamegraph
cargo flamegraph --bin my-app

// ❌ Allocates each iteration
for s in strings {
    result = result + &s;
}

// ✅ Pre-allocate
let mut result = String::with_capacity(total_len);
for s in strings {
    result.push_str(&s);
}

// ❌ Intermediate collection
let v: Vec<_> = data.iter().map(|x| x * 2).collect();
let sum: i32 = v.iter().sum();

// ✅ Lazy chain
let sum: i32 = data.iter().map(|x| x * 2).sum();

use std::borrow::Cow;

fn process(input: &str) -> Cow<str> {
    if input.contains("bad") {
        Cow::Owned(input.replace("bad", "good"))
    } else {
        Cow::Borrowed(input)
    }
}

[profile.release]
lto = true
codegen-units = 1
opt-level = 3