Quoting from https://doc.rust-lang.org/nightly/std/vec/struct.Vec.html#method.extend_from_slice

Note that this function is same as extend except that it is specialized to work with slices instead.

But Vec::extend_from_slice supports &[T] for T: Clone, whereas Vec::extend only supports impl Iterator<Item = &T> if T: Copy, so it’s not the same.