Build HashSet from a vector in Rust

I want to build a HashSet from a Vec. I'd like to do this

• in one line of code,

• copying the data only once,

• using only 2n memory,

but the only thing I can get to compile is this piece of .. junk, which I think copies the data twice and uses 3n memory.

fn vec_to_set(vec: Vec) -> HashSet {
    let mut victim = vec.clone();
    let x: HashSet = victim.drain(..).collect();
    return x;
}

I was hoping to write something simple, like this:

fn vec_to_set(vec: Vec) -> HashSet {
    return HashSet::from_iter(vec.iter());
}

but that won't compile:

error[E0308]: mismatched types
--> :5:12
|
5 | return HashSet::from_iter(vec.iter());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u8, found &u8
|
= note: expected type std::collections::HashSet
= note: found type std::collections::HashSet


.. and I don't really understand the error message, probably because I need to RTFM.

Because the operation does not need to consume the vector¹, I think it should not consume it. That only leads to extra copying somewhere else in the program:

use std::collections::HashSet;
use std::iter::FromIterator;

fn hashset(data: &[u8]) -> HashSet {
    HashSet::from_iter(data.iter().cloned())
}

Call it like hashset(&v) where v is a Vec or other thing that coerces to a slice.

There are of course more ways to write this, to be generic and all that, but this answer sticks to just introducing the thing I wanted to focus on.

¹This is based on that the element type u8 is Copy, i.e. it does not have ownership semantics.

Stack Overflow Q#39803237, score: 98