Basic benchmark.

main.rs

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

#[derive(Debug, Eq, PartialEq)]
enum AOrB {
    A(String),
    B(String),
}

impl AOrB {
    fn swap_take_mut(&mut self) {
        use self::AOrB::*;
        take_mut::take(self, |old| match old {
            A(s) => B(s),
            B(s) => A(s),
        });
    }

    fn swap_replace_with(&mut self) {
        use self::AOrB::*;
        replace_with::replace_with_or_abort(self, |old| match old {
            A(s) => B(s),
            B(s) => A(s),
        });
    }
}

fn criterion_benchmark(c: &mut Criterion) {
    c.bench_function("take_mut", |b| b.iter(|| {
        let mut a_or_b = AOrB::A("Hello World!".to_owned());
        a_or_b.swap_take_mut();
        // assert_eq!(a_or_b, AOrB::B("Hello World!".to_owned()));
    }));
    c.bench_function("replace_with", |b| b.iter(|| {
        let mut a_or_b = AOrB::A("Hello World!".to_owned());
        a_or_b.swap_replace_with();
        // assert_eq!(a_or_b, AOrB::B("Hello World!".to_owned()));
    }));
}

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