From iterator to Vec should be possible

[Mec-iS]

I'm submitting a

• [x] feature request.

Current Behaviour:

Looks to me that mutable iterators build with Array::iterator_mut cannot be collected back to a Vec:

use smartcore::linalg::basic::arrays::Array;
let element_2: &i32 = vec![1, 2, 3].iterator_mut(0).collect::<Vec<i32>>().get(1).unwrap();
println!("mutable iterator: {:?}", *element_2);

This code raise this compiler error:

[E0277] Error: a value of type `Vec<i32>` cannot be built from an iterator over elements of type `&mut {integer}`
    ╭─[command_48:1:1]
    │
 21 │ let element_2: &i32 = vec![1, 2, 3].iterator_mut(0).collect::<Vec<i32>>().get(1);
    ·                                                     ───┬───  
    ·                                                        ╰───── value of type `Vec<i32>` cannot be built from `std::iter::Iterator<Item=&mut {integer}>`

Maybe we need to implement FromIter for Vec? there are any caveats because this should not be possible?

Expected Behaviour:

Should be possible to collect an iterator build from Array::iterator and Array::iterator_mut back into a Vec

[flixstn]

Hey, I found your machine learning library, gave it a try and it looks awesome! So I went through the issues and thought maybe I can contribute to one or two tickets. The standard library basically provides three methods for iterating over a collection: iter(), which iterates over &T iter_mut(), which iterates over &mut T into_iter(), which iterates over T

Since Array::iterator and Array::iterator_mut cover the first two cases, calling collect::<Vec<i32>>() won't work since the trait FromIterator<T> is implemented for Vec<T>, not for &T so we would have to either implement into_iter() to move ownership to a new Vec<T> or simply call collect::<Vec<&T>> to keep ownership and having references. (Or maybe we can do some tricks by calling clone internally?) So calling: let vec = vec![1,2,3].iterator(0).collect::<Vec<&i32>>() would work and we can get values by simply calling let elem = vec![1,2,3].iterator(0).collect::<Vec<&i32>>().get(1).

[Mec-iS]

thanks for using smartcore.

we will be glad to take a look to a PR for this or anything else you want to contribute.

P.S. we would like to keep the zero-copy policy when possible.