When does the IntoIterator implementation for mut Vec get invoked?

Question

The Vec type has an implementation of the IntoIterator trait for mutable vectors:

impl<'a, T> IntoIterator for &'a mut Vec<T> {
    type Item = &'a mut T;
    type IntoIter = slice::IterMut<'a, T>;

    fn into_iter(self) -> slice::IterMut<'a, T> {
        self.iter_mut()
    }
}

I am not able to get that code invoked. I am trying:

let mut vec = vec![1, 2, 3];
for mut i in &vec {
    println!("{}", i);
}

What usage of Vec will invoke that particular IntoIterator implementation?

I think you should call directly wiht _vec.into_iter()_. You don't need to have the vec mutable for that, and even the item _i_ don't need to be mutable, as you're going to have ownership of the vector's items. — Mario Santini, Aug 31 '20 at 12:05
I think I figured it out. Have added an answer to my own question. — pramodbiligiri, Aug 31 '20 at 12:17
`mut Vec` is not a type. There is an implementation of `IntoIterator` for `&mut Vec`, and one for `Vec`, as well as the one for `&Vec` which is the one you are calling in this code. — trent, Aug 31 '20 at 13:09

score 2 · Accepted Answer · edited Dec 25 '20 at 18:41

2

The following code will invoke the IntoIterator variant mentioned in the question:

let mut vec = vec![1, 2, 3];
for i in &mut vec {
    println!("{}", i);
}

This is because the vec! macro returns an owned Vec, not a reference. You can mutably iterate over the owned Vec using for i in &mut vec.

edited Dec 25 '20 at 18:41

pretzelhammer

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answered Aug 31 '20 at 12:17

pramodbiligiri

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The `vec!` macro returns an owned vector, not a reference. You can mutably iterate over the owned vector `vec` using `for i in &mut vec`. – Sven Marnach Aug 31 '20 at 12:31
Updated the answer with the info you provided. – pramodbiligiri Aug 31 '20 at 12:36

When does the IntoIterator implementation for mut Vec get invoked?

1 Answers1

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