In Rust, is a vector an Iterator?

Question

Is it accurate to state that a vector (among other collection types) is an Iterator?

For example, I can loop over a vector in the following way, because it implements the Iterator trait (as I understand it):

let v = vec![1, 2, 3, 4, 5];

for x in &v {
    println!("{}", x);
}

However, if I want to use functions that are part of the Iterator trait (such as fold, map or filter) why must I first call iter() on that vector?

Another thought I had was maybe that a vector can be converted into an Iterator, and, in that case, the syntax above makes more sense.

Answer 1

No, a vector is not an iterator.

But it implements the trait IntoIterator, which the for loop uses to convert the vector into the required iterator.

In the documentation for Vec you can see that IntoIterator is implemented in three ways:

• for Vec<T>, which is moved and the iterator returns items of type T,
• for a shared reference &Vec<T>, where the iterator returns shared references &T,
• and for &mut Vec<T>, where mutable references are returned.

iter() is just a method in Vec to convert Vec<T> directly into an iterator that returns shared references, without first converting it into a reference. There is a sibling method iter_mut() for producing mutable references.