Questions And Answers

More Tutorials

What is the difference between iter and into_iter in Rust?

The iterator returned by into_iter may yield any of T, &T or &mut T, depending on the context.
The iterator returned by iter will yield &T, by convention.
The iterator returned by iter_mut will yield &mut T, by convention.

into_iter comes from the IntoIterator trait, Example:

pub trait IntoIterator 
    <Self::IntoIter as Iterator>::Item == Self::Item, 
    type Item;
    type IntoIter: Iterator;
    fn into_iter(self) -> Self::IntoIter;

You implement this trait when you want to specify how a particular type is to be converted into an iterator. Most notably, if a type implements IntoIterator it can be used in a for loop.

Each variant is slightly different.

This one consumes the Vec and its iterator yields values (T directly):

impl<T> IntoIterator for Vec<T> {
    type Item = T;
    type IntoIter = IntoIter<T>;

    fn into_iter(mut self) -> IntoIter<T> { /* ... */ }

The other two take the vector by reference (don't be fooled by the signature of into_iter(self) because self is a reference in both cases) and their iterators will produce references to the elements inside Vec.

This one yields immutable references:

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

    fn into_iter(self) -> slice::Iter<'a, T> { /* ... */ }

While this one yields mutable references:
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> { /* ... */ }

into_iter is a generic method to obtain an iterator, whether this iterator yields values, immutable references or mutable references is context dependent and can sometimes be surprising.

iter and iter_mut are ad-hoc methods. Their return type is therefore independent of the context, and will conventionally be iterators yielding immutable references and mutable references, respectively.


In this page (written and validated by ) you learned about What is the difference between iter and into_iter in Rust? . What's Next? If you are interested in completing Rust tutorial, we encourage you simply to start here: Rust Tutorial.

Incorrect info or code snippet? We take very seriously the accuracy of the information provided on our website. We also make sure to test all snippets and examples provided for each section. If you find any incorrect information, please send us an email about the issue:

Share On:

Mockstacks was launched to help beginners learn programming languages; the site is optimized with no Ads as, Ads might slow down the performance. We also don't track any personal information; we also don't collect any kind of data unless the user provided us a corrected information. Almost all examples have been tested. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. By using, you agree to have read and accepted our terms of use, cookies and privacy policy.