gistfile1.txt

extern crate time;

// Single array of 10 000 000 will cause stack overflow, so outer and inner
const size_outer:usize = 1000;
const size_inner:usize = 10 * 1000;

fn create_vec() -> Vec<[usize;size_inner]> {
    let mut data:Vec<[usize;size_inner]> = Vec::with_capacity(size_outer);
    for _ in 0..size_outer {
        data.push([0usize;size_inner]);
    }
    data
}

fn without_as_ref(data: Vec<[usize;size_inner]>) {
    let t0 = time::precise_time_ns();
    {
        let result : Result<_,usize> = Ok(data);
        match result {
            Ok(data1) => {},
            Err(_) => {}
        }
    }
    let t1 = time::precise_time_ns();
    println!("without_as_ref duration={}", (t1 - t0));
}

fn with_as_ref(data: Vec<[usize;size_inner]>) {
    let t0 = time::precise_time_ns();
    {
        let result : Result<_,usize> = Ok(data);

        match result.as_ref() {
            Ok(data1) => {},
            Err(_) => {}
        }
    }
    let t1 = time::precise_time_ns();
    println!("with_as_ref duration={}", (t1 - t0));
}


pub fn main() {
    let v1 = create_vec();
    let v2 = create_vec();
    with_as_ref(v1);
    without_as_ref(v2);
}

Results:

with_as_ref duration=7977913
without_as_ref duration=8698716