Pass [[f64]] reference to function

help
1

Hello everyone,

Is it possible to passe a [[f64]] by reference to a function ? For example :

const N: usize = 100;

let a: [[f64;N];N] = [[0.0;N];N];

my_function(&a)

I know this code will not compile, but it exists a way to do the same efficiently ?

I have the same question to a [[[f64]]] array.

Just another question : is it true that vector has less fast as array in Rust ?

Thank you !

2

No you cannot

Yes, vectors are slower than arrays, but you will likely never see them in your profiler, so I wouldn't worry about it.

Also Rust doesn't support arrays thar well yet, so it will be much easier to use vectors.

3

Okay, thank you !

4

right, for

fn my_function(a: &[[f64;N];N]) {
}

it does need to know N in advance, there's currently no way to parameterize the function type over different array sizes, this would need const generics

&[[f64;N];N] doesn't automatically coerce to a slice of slices [[f64]] because it has a very different representation, if you have

fn my_function(a: &[&[f64]]) {
}

then to call it, you'd need to generate an vector (or array) of slices first

fn main() {
    let a: [[f64;N];N] = [[0.0;N];N];
    let rows = a.iter().map(|x| &x[..]).collect::<Vec<_>>();
    my_function(&rows);
}

not with regard to access, as far as i know—both an array and a vector lay out the elements consecutively in memory—the difference in performance is that a Vector requires a separate heap allocation to create, whereas arrays are allocated on the stack (or as part of the structure they're part of)

5

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