I’m new to Rust. And now I have some problems in understanding slice. Of course, slice is very easy to use and understand. But I don’t know the reason why does rust need us to use slice in this way.

In the tutorial, when explain &str is the slice reference to str. str is the slice. And we can create a slice like this

let string: &str = "a string";
let arr:[i32; 4] = [1,2,3,4];
let arr_slice:&[i32] = &arr[..2];

Here, I think, the size of slice is quite clear. arr_slice has referenced to two i32 elements. If I understand it in C, it will look like:

typedef struct {
void* ptr;
int length;
} slice;

The length can be known through the slice syntax [...]. Thus, size of slice can also be inferred by sizeof(type of ptr) * length which behaves like array. So that in the example above, it’s very easy to know the size of slice itself at compile time.

Why does Rust make slice a DST?