reflect_access.rs

use bevy::prelude::*;

fn main() {
    divan::main();
}

#[divan::bench]
fn reflect() {
    let mut input: Box<dyn MovementField> = Box::new(PlayerInput::default());
    for n in 1..=1000 {
        input.get_movement_mut().x += 10.;
        assert_eq!(input.get_movement().x, n as f32 * 10.);
    }
}

#[derive(Reflect, Default, Debug)]
struct PlayerInput {
    movement: Vec2,
}

trait MovementField {
    fn get_movement(&self) -> &Vec2;
    fn get_movement_mut(&mut self) -> &mut Vec2;
}

impl<T> MovementField for T where T: GetField {
    fn get_movement(&self) -> &Vec2 {
        self.get_field("movement").unwrap()
    }

    fn get_movement_mut(&mut self) -> &mut Vec2 {
        self.get_field_mut("movement").unwrap()
    }
}

trait_access.rs

use bevy::prelude::*;

fn main() {
    divan::main();
}

#[divan::bench]
fn access() {
    let mut input = PlayerInput::default();
    for n in 1..=1000 {
        input.get_movement_mut().x += 10.;
        assert_eq!(input.get_movement().x, n as f32 * 10.);
    }
}

#[derive(Reflect, Default, Debug)]
struct PlayerInput {
    movement: Vec2,
}

trait MovementField {
    fn get_movement(&self) -> &Vec2;
    fn get_movement_mut(&mut self) -> &mut Vec2;
}

impl MovementField for PlayerInput {
    fn get_movement(&self) -> &Vec2 {
        &self.movement
    }

    fn get_movement_mut(&mut self) -> &mut Vec2 {
        &mut self.movement
    }
}

Updated to use trait object in reflect benchmark

access     fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ access  949.7 ns      │ 1.862 µs      │ 949.7 ns      │ 962.3 ns      │ 100     │ 1600
reflect     fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ reflect  943.5 ns      │ 1.206 µs      │ 956 ns        │ 963 ns        │ 100     │ 1600