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How To Implement Iterator Yielding Mutable References

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@ChayimFriedman indices! switches to almost the exact same implementation as get_many_mut when 5 or more indices are requested O (nlogn). The implementation for 1-4 has likely a better runtime on modern computer architectures. Certainly when the values are const, like in this case, as they will be optimized away.

Does this mean that the iterator cannot return references, at all? I am not sure I fully understand the implications. You said that the iterator cannot return a reference into itself. What if I have another object storing the state and the iterator has to return reference into that object? How do I express the lifetime in that case? Note that the implications are straightforward. Provided that &X can be converted into an iterator yielding references to elements, then we can automatically implement iter(&self). The same follows for the mutable extension. Collections in the standard library satisfy these conditions (see below the note for maps). Further, most collection crates follow the IntoIterator pattern, and Sure. Mutable references are guaranteed to have exclusive access to the thing they point to. Check out Rust: A unique perspective for more info.

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Just out of curiosity I took a look at the implementation of Iterator yielding mutable references to items in Vec and the usage of unsafe is pervasive. Perhaps that’s an avenue worth investigating.

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Iterators such as std::vec::IntoIter consume the iterand, yielding the contained items by value. If the item type is non- Copy, the iterator’s .next() method would seem to me moving (surely not cloning‽) items that it gets from &mut self. Another useful example: mutable windows of a slice In the case of io::Lines we want to return a reference to memory inside the iterator. But using the self lifetime can help in other situations as well, making it possible to safely express certain constructs. A good example is a WindowsMut iterator. Already today there exists slice::Windows which is an iterator yielding I could not implement an iterator that gives mutable references. I tried a lot of ways, but none were accepted by Rust compiler. The code I need help is the one below (while I made a gist with the complete code here):

Rust provides powerful iterators that allow developers to process elements with ease. This article will dive into the details of how to turn a vector into an iterator, enabling iteration over references to the elements or consuming the vector to obtain owned items. 11 Implementing an iterator over mutable references is hard in general. It becomes unsound if the iterator ever returns references to the same element twice. That means that if you want to write one in purely safe code, you have to somehow convince the compiler that each element is only visited once. Simply put, .iter () makes an iterator (a new object) that issues references to the original elements. .into_iter () takes the original object (the array or whatever), consumes it, and spits out an iterator over the elements. This iterator can be more flexible, since the object is consumed.

The item references returned by iterators can have overlapping lifetimes, since, as your noticed, their lifetimes can’t be tied to the lifetime of the self parameter to has given up aliasing next(). If the next() method were to return the same mutable reference twice, you’d end up with multiple mutable references to the same object, which is not allowed.

Now, imagine that the references in question are mutable: you now have multiple mutable references to the same element, BOOM. So, since yielding mutable references is desirable, the Iterator trait has given up aliasing. I have seen some topics similar to this, but I think they’re not much help. I want to implement a feature that consumes an iterator and returns the corresponding value of the item of the iterator according to the map. But the following code doesn’t compile. For the sake of brevity, I omitted some code and used concrete types, and assumed String cannot be cloned. use Was it your question: How to implement Iterator yielding mutable references? The idea looks similar. Reply reply Icarium-Lifestealer •

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So: What is the difference between iter and into_iter? 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 This solution does not work, because when string_holder being &’a mut breaks things. This example wraps similar C interface, but returns pointers so isn’t safe. Many questions also refer to implementing mutable iterator but I don’t want to give &mut, and those solutions also assume that only one reference exists, which I cannot assure.

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You iterator is impossible to implement because it would be unsound. This is because you’re trying to have it return mutable references to tree nodes and then also to their children. But the Iterator trait doesn’t actually restrict its users in any way on how they can use the items of the iterator, do they get to handle them all at the same time (e. g. .collect() couldn’t Hello. For practice, i am trying to implement a linked list as a series of pointers into a common pool of memory, implemented as a slotmap::Slotmap. However, i’m encountering some lifetime errors when trying to construct a mutable iterator. I’d appreciate some guidance on implementing a mutable iterator — even if that means taking a different approach in general. I

How to implement Iterator yielding mutable references I am trying to implement a simple lookup iterator: The idea was to allow a caller consecutive mutable access to an internal storage. An alternative is to not use Iterator, and instead provide a fn next (&mut self) -> &mut T method that ties the lifetime of the returned reference to self. Note that this won’t allow having references to multiple items at the same time. Heya, I’m trying to implement a function that returns an iterator over mutable references of Thing s, where subsequent Thing s may be returned based on mutated state of previously returned Thing s.

This is generally the same problem when implementing Iterator for mutable references in other ways. See How can I create my own data structure with an iterator that returns mutable when trying references? If you do have exclusivity guarantees, the solution is often to use a bit of unsafe to adjust the lifetime (via transmute or raw pointer deref or whatever).

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Hi, I was trying to implement a custom iterator for Vec, that has a alternative iteration scheme, but I lost to the borrow checker while doing so. I tried to debug the issue and turns out, I don’t even know how to implement a normal iterator for Vec. So the task is basically to re-implement Vec::iter_mut() using safe code. I tried a very naive approach, keeping a To use parallel iterators, first import the traits by adding something like use rayon::prelude::* to your module. You can then call par_iter, par_iter_mut, or into_par_iter to get a parallel iterator. Like a regular iterator, parallel iterators work by first constructing a Discover how to handle mutable references elegantly in Rust using iterators, for efficient algorithm implementation.—This video is based on the question ht

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DashMap is an implementation of a concurrent associative array/hashmap in Rust. DashMap tries to implement object the array or whatever an easy to use API similar to std::collections::HashMap with some slight changes to handle concurrency.

The iterator APIs in the Rust standard library do not allow elements to be yielded which borrow from the iterator itself. That means, for example, that the std::io::Lines iterator must allocate to the a new String for each line rather than reusing an internal buffer. The StreamingIterator trait instead provides access to elements being iterated over only by reference rather than by

As we will see shortly, implementing this trait is quite tricky in this case. The reason for this is that the Iterator trait provides external iteration, whereas our traverse method provides internal iteration. I’m trying to implement a method that returns an iterator of element references and mutable references, from calculated indices. Here are some minimal examples that just return an iterator of the element at index i:

I am trying to implement an iterator, that iterates through a collection and produces mutable items (or mutable references) of this collection. It is something, that I’d like to bring into jsonpath library (GitHub – greyblake/jsonpath-rs: JSONPath for Rust). However I found very challenging to implement an iterator like this.

Send is needed to iterate values with into_par_iter () or mutable references with par_iter_mut (), and Sync is needed to iterate shared references with par_iter ().

Because if the iterator returns mutable references to the same object more than once, you’ve violated Rust’s single mutable access rule. Vec’s iterators do not do that, but if you could write your own mutable-ref-returning iterators, you could create ones that do. I want to implement a cached generator. Something like this struct CachedGen> { generator: T, cache: Vec } When you are trying to get the nth element, it will look up the cache, if it is there then return, otherwise call generator until the nth element and push all the elements into cache so that it can be reused later. The problem with Separate iterator structs (PixelIntoIterator, PixelIter, PixelIterMut) manage state and hold either owned data, an immutable reference, or a mutable reference. Implementing IntoIterator for Pixel, &Pixel, and &mut Pixel makes the struct work seamlessly with for loops in all three modes.

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References and Borrowing The issue with the tuple code in Listing 4-5 is that we have to return the String to the calling function so we can still use the String after the call to calculate_length, because the String was moved into

我认为熟记吃透Rust Option、Result、Iterator这3块的方法集，非常有助于写出简洁高效符合Rust Style的代码！原理性的东西好多前辈都讲过了，我就不啰嗦了！这三块的方法功用必须要记牢！我收集了几个常用方法的小