With a 1 dimensional array it is possible to convert from a fixed sized array to a slice but is this possible with 2d array in a trivial way?
fn foo(r: &[&[usize]]) { }
let r = [[0usize; 10]; 10];
foo(&r); //<== error expected type `&[&[usize]]` found type `&[[usize; 10]; 10]`
There is no trivial way of doing this (for some definition of trivial). The problem is that &[&[usize]] is a slice of slices (like a jagged array), while [[0usize; 10]; 10] is a 2D array. The data in a 2D array is contiguous, a line starts after the end of the previous line and all lines have the same number of elements. In a jagged array, each line can have a different length, and this length must be stored with each line (in Rust, a slice is a length and a pointer).
That said, you can change the definition of foo (this is the best alternative, because there is no extra allocation):
// a slice of T, where T can be used as &[usize]
fn foo<T>(r: &[T])
where T: AsRef<[usize]>
{
for line in r {
println!("{:?}", line.as_ref());
}
}
fn main() {
let r = [[0usize; 10]; 10];
foo(&r);
}
or create a temporary vector of slices:
fn foo(r: &[&[usize]]) {
for line in r {
println!("{:?}", line);
}
}
fn main() {
let r = [[0usize; 10]; 10];
let x: Vec<&[usize]> = r.iter().map(|v| v.as_ref()).collect();
foo(&x);
}
