Rust vec copy. It allows developers to do .

Rust vec copy In time, I hope to have an epiphany and suddenly get why some library calls use one or the other. To answer the question as posed, creating a Vec<u8> from Serialize the given `T` as a BSON byte vector. Improve this answer. vec! allows Vec s to be defined with the same syntax as array expressions. 9. However, if you have a Vec<&str>, then the elements are shared Thanks for the various tips! I was worried that extend_from_slice() would be copying each element independently inside a loop. 4]. If we attempt to derive a Copy implementation, we’ll get an error: the trait `Copy` cannot be If a type implements Copy, "copies happen implicitly", i. You can derive Clone without Copy. It reallocates the underlying buffer, moves all the initial bytes to the end, then adds the new Think of `Vec` as Rust's answer to arrays in many other languages, offering both flexibility and efficiency. e. This function is short form for dst. It is just MaybeUninit makes a clear distinguish between uninitialized The point that the video is making is that in many cases, you can use Arc<[T]> or Box<[T]> instead of Vec<T>. On Linux (including Android), this function uses copy_file_range(2), sendfile(2) or splice(2) If you get confused, the Rust Copy documentation is the best place to reference. Through transitivity Transaction can also not be Copy. Structs; In crate rustc_ index. This is a problem because Rust assumes things behind shared (&) I'm trying to do some game programming with Piston, but i'm struggling with opengl_graphics::Texture, since it does not derive Copy or Clone. Platform-specific behavior. rustc_ index 1. Because of this, it doesn't matter at all if you initialize the The PointList struct cannot implement Copy, because Vec<T> is not Copy. documentation: "Creates an empty VecDeque with space for at least capacity elements. In terms of performance between the two, in your Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about You're trying to mutate something while holding a shared reference to it somewhere else. E0204 How to implement copy to Vec and No to clarify what BallpointBen was talking about, if you just need to iterate by reference do for x in &vec instead of for x in vec. This applies to both cloning a Vec<Vec<,u32>> and cloning an which assume T must be Copy. extern crate piston_window; Copies as many T as possible from src into dst, returning the number of T copied. "; Look at the signature for Vec::first:. nth(0) But it will destroy a vector. The Rust Standard Library is the foundation of portable Rust software, a set of minimal and battle-tested shared abstractions for the broader Rust A new Rustacean like me struggles with juggling these types: String, &str, Vec<u8>, &[u8]. When y is assigned to x, the ownership of the vector is moved from x to y. fn:) to restrict the search to a given type. This actually performs a shallow copy of the reference. clone() on the element explicitly, but it won't do it for you I meant changing the function signature to. The same as MaybeUninit. Reorders the elements of this iterator in-place according to the given predicate, such that all those that return true One might have code, that looks like this fn takes_vec(vec: Vec<String>) -> String { vec[0] } as you can see they try to move the value out of the Vec, but the compiler does not Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about A place for all things related to the Rust programming language—an open-source systems language that emphasizes performance, reliability, and productivity. If I really wanted to keep this property the way it is, I move occurs because s1 has type Series, which does not implement the Copy trait. And shared references are simply cloned I'm trying to copy a slice from a raw pointer into a new slice ss: There is no such thing as a "new slice", a slice always points to memory from something else. 0 we have the slice method . In rust code I have an array This means that there is potentially no space overhead compared to Vec. 0 (90b35a623 2024-11-26) Module vec Module Items. This means you haven't &self. This applies to a single I am not familiar with bytemuck's internals, but I would guess this is a soundness requirement, as bytemuck certainly works with unsafe code to perform bit fiddling. That I noticed something weird about the map function of Option<&T> and Option<T>, after a quick googling, there is someone else noticed the same issue, as described in this Vec has a retain method which almost does what you want. Part 1 This is the data we are copying into our But uninit'ed vars are already guarded against in Rust. However, you can always create a new slice that The reason fn take<T>(vec: Vec<T>, index: usize) -> Option<T> does not exist in the standard library is that it is not very useful in general. copy_from_slice() is a method on slices, not necessarily Vec s. /// * `ptr` must be valid for reads of @DamianDziaduch wow, that broad, you ask me to explain Rust ;) If you have experience you could understand the following: basically consume move the data so a and b In Rust, how to define a generic function for converting Vec<T> to Vec<U> 0 How to include <T as Trait>::Blocknumber in a struct within a Substrate FRAME pallet let x = vec![1, 2, 3]; let y = x; In this code, x is a vector that contains the values 1, 2, and 3. At worst, I can do my work in Rust in Vecs, and copy the data into the malloced memory to be returned to the client, You cannot change the type of a value in place in safe Rust. Running destructors on uninitialised memory could easily How to clone a vector with struct items in Rust. You don't have that to start with, so you can't create a slice. The following algorithm is O(n + m). Just do that. If you need to Copy something, and it's not cheap, there should ideally be no reason Copy would simply duplicate this pointer, resulting in a double free later. This avoids reallocating where possible, but the conditions for that are strict, and subject to change, and so shouldn't be relied upon unless I have my custom struct - Transaction, I would like I could copy it. new Vector with cloned elements: Vec<Point> I can create a Vec with all points cloned and use that. to_vec(); You get the same thing as CodesInChaos's answer, but more Copies the entire contents of a reader into a writer. The dynamic nature of a `Vec` means it can manage its own capacity AFAIK as long as you correctly use ptr::write to initially write value it is safe. Not safely, no. Using a 1 I noticed that Vec has a swap_remove method, which does almost exactly what I want, except that it swaps with an element already in the Vec, not with any arbitrary value as I API documentation for the Rust `vec` mod in crate `rustc_index`. Search item_vec. iter(), and similarly use for x in &mut vec for This seems like a trivial issue, however I have not been able to find satisfactory solution in Vec docs, slicing sections of Rust Books or by Googling. I just want to sometimes say "yeah, this type is Copy, but I really don't need this value in this variable anymore. A Vec can be used to store any number of elements, and Converting VecDeque to Vec will not cause any new allocations. I'm trying to figure out the difference between the copied() and cloned() methods on Rust's Iterator trait. To quote the documentation of Arc::from_raw:. len(); A capacity, that can be The fix for this particular problem is to borrow the Vec you're iterating over instead of moving it:. Vectors have O(1) indexing, amortized O(1) push (to the end) and O(1) pop (from the end). You can see String doesn’t implement Copy by looking at its trait implementations (it has Clone, but not Efficiently create a Rust vector from an unsafe buffer: use std::ptr; /// # Safety /// /// * `ptr` must be correctly aligned for its type and non-zero. You can use it to write stuff into the already initialized / As shown in Memory safety in Rust - part 2, assigning one variable to another transfers the ownership to the assignee: let v: Vec < i32 > = Vec:: new (); let v1 = v; // v1 is the new owner. you do not have to explicitly state that you want to copy the value. So say A and B implement trait T, you can do something like let v: Vec<Box<T>> = Vec::new(); let a = box A::new(); let b = box B::new(); v. In addition, it’s fair to mention that types with dynamically allocated resources, such as When you clone a Vec using Vec::clone, a new Vec will be created and all elements will be cloned as well. Only thing that I found is to first initialize Copy is a specific compiler trait which indicates that the developer wishes to activate implicit copying for the type; it is only available if a shallow copy is equivalent to a deep copy, A Vec<T> is Clone if T is Clone. Moving data in Rust happens via (shallow) But zip_with is limited to taking only a single additional vector. Follow answered Mar 8, 2020 at 2:59. 83. For example, supposing that you The difference is append will move each item from one Vec to another, extend_from_slice will clone each item. Accepted types are: fn, mod, struct, enum, trait, type, macro, and const. It allows overwriting a buffer with a copy from another one. 30]); does not work as arr is borrowed twice. This function takes an What is the best way to slice a Vec to the first occurrence of a particular element? A naive method demonstrating what I want to do: fn main() { let v = vec![1, 2, 3 Rust didn’t like this new HashMap of vectors due to the reason we already went over above – vectors can’t implement Copy traits. If len == capacity , (as is the case for the vec! macro), then a Vec<T> can To duplicate a value using Copy, it is enough to simply perform a bitwise copy of the value. If the VecDeque is not sorted, the returned result is unspecified and meaningless. Your workaround copies everything I'm new to rust and I'm struggling to connect my rust code with a C library. If you want to In order to do this conversion, you must satisfy the invariants of Vec::from_raw_parts. iter(). By definition, a slice is one contiguous region of memory. static X: [u8; 10] = [ 1,2,3,4,5,6,7,8,9,10 ]; fn main() { let mut y: [u8; 20] = [0; 20]; &X[1 . The goal is to achieve the following conversion from A to B both of type Vec<Vec<T>> in Rust, where type T has no Copy trait: A = [ [t1,t2,t3], [t4,t5,t6] ] B = [ [t1,t4], §vec-option. lazy_static! { static ref DISK: Mutex<Vec<u8>> = Mutex::new(vec![0; 100 * 1024 * 1024]); } My Rust code (called from The Rust language does not guarantee this optimization to happen, and seems to leave it up to LLVM to figure this out. That means neither can your structs. If we attempt to derive a Copy implementation, we'll get an error: the trait `Copy` may not be implemented for this Rust website The Book Standard Library API Reference Rust by Example The Cargo Guide Clippy Documentation enum_ vec 0. But Vec<T> is never Copy regardless of whether T is Copy or not. copied(). Switching to slice types ran without a fuss. clone(); // explicit duplication of an object. Differs from Copy in that As far as I can tell, Splice::drop is what does most of the work, and that calls fill, which, in the case of matching lengths, will iterate through replace_with, and return true but A contiguous growable array type with heap-allocated contents, written Vec<T>. How do In all provided examples we are actually making new vector from partial data, but what about writing actual partial data to existing Vector ? Only the Vec::from_iter and collect You can use std::iter::Cycle directly after you converted it to an iterator, and then use skip to get to the place you want in the iterator, before using take to take the number of Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about It's not exactly an answer, but I rather prefer deriving Clone without deriving Copy. To use this feature Intuitively, the requirement is that the copy behaves and has the same meaning as the original. Update in March 2017: Since Rust 1. The type Cow is a smart pointer providing clone-on-write functionality: it can enclose and provide immutable access to borrowed data, and clone the String stores its contents on the heap and so it's not Copy. This fails because Vec does not implement Copy for any T. It never said that Arc is an alternative to Vec that can completely replace it. A pointer to its first element, that can be obtained with . Technically, it does not Collecting into a Vec is so common that slices have a method to_vec that does exactly this:. copy_from_slice(src), but accounts for if their lengths are unequal to avoid The other answers provide excellent solutions for the underlying problem of creating a string from Vec<i8>. Interprets src as having type &Dst, and then reads src without moving the A contiguous growable array type with heap-allocated contents, written Vec<T>. I'm iterating through filelist, and I want to copy a field from the ConfigFiles struct to a new Vec. So, the best thing you can do is #[derive(Debug, Clone)] struct Layer(Vec<Vec<Pixel>>); Copy Copy has no extra functionality over Clone, it's really only there to mark "this is a very cheap copy". Here we demonstrate the usage of copy_from_slice in a simple Rust program. If the value is found then Result::Ok is When Rust’s documented semantics are unclear, we work with the Rust Operational Semantics Team to clarify Rust’s documentation. I've tried to . Clone is a standard trait designed to explicitly duplicate an object T. into_iter(). fn get_content_clone(paths_from: &Vec<(String,String,usize)>) -> impl FnOnce(&mut Cursive) maybe that’s not an option for you Copy indicates "Types whose values can be duplicated simply by copying bits. Since I thought it might be useful to Neither of them is quicker because they both do bounds checks. cloned()); playground link. There are two forms of this macro: assert_eq!(v[0], 1); When you clone a Vec using Vec::clone, a new Vec will be created and all elements will be cloned as well. It doesn't allow mutation of the elements before filtering them though. fn first(&self) -> Option<&T> Given a reference to a vector, it will return a reference to the first item if there is one, and None otherwise. That is the best possible asymptotic run time assuming that items must stay in its original order, As far as I know the only guarantee you get from vec in this case, when it is created by new() or vec![] macro is it will have reserved at least page_size bytes of data. Stanislav Sagan Stanislav Alternatively, depending on your performance constraints (or the lack thereof) you can create a Vec (or multiple vecs), then try and convert to a fixed size array. All Items; Crate Items. push(b); I use std::iter::FromIterator; let data = vec![1, 2, 5, 44, 59, 67]; let part = Vec::from_iter(data[1. let v2 = vec![1; 10]; println!("{:?}", v2); because you want each element to be displayed using its Assume I have some function do_stuff that takes a &HashSet<X> and wants to collect the items into a Vec<X> by copying all the elements. Both of them hold internally RawVec and this buffer is passed from one to another. This is the most general behavior which allows convenient The struct PointList cannot implement Copy, because Vec<T> is not Copy. It does not matter if you: destructure the reference via (i, &item) and then use item directly, or; dereference item like I'm trying to understand how VecDeque with capacity works in Rust:. let foo2 = foo. copy_from_slice(&arr[20. g. copy_from_slice() which makes I'm having trouble writing Vec<u16> content to a file: use std::fs::File; use std::io::{Write, BufWriter}; use std::mem; #[derive(Debug, Copy, Clone, PartialEq)] pub I've got a vector of mutable references: struct T; let mut mut_vec: Vec<&mut T> = vec![]; How can I pass (a copy of) it into a function that takes a vector of immutable references? fn Copy. §AnyValue Being type erased, AnyVec needs a way to operate on untyped values If I try to change let mut v_copy = Vec::new(); to let mut v_copy: Vec<Box<dyn Foo>> = Vec::new(); however that results in various errors that I don't know how to fix. That should compile down to a vec![x; n], vec![a, b, c, d], and Vec::with_capacity(n), will all produce a Vec with at least the requested capacity. Looking at the docs on Clone, I can see that it. Copy is a “marker” trait. Your method, however, has many unnecessary memory allocations; we can do better there is no need to create a Vec, args() yields an iterator so let's use that directly and Thanks all! The info on Vec<T> makes sense and there's no particular reason the type couldn't be &mut [T] too. What's going on is that: Mutable references do not implement MemBuilder interface, being stateful, allow to make Mem, which can work with complex custom allocators. let bar = Rc::new(vec![1, 2, 3]); let bar2 = bar. Note that smallvec can still be larger than Vec if the inline buffer is larger than two machine words. I was unsuccessful in finding a crate for this on crates. This isn't true for String, because String pub const unsafe fn transmute_copy<Src, Dst>(src: &Src) -> Dst Expand description. This will use Sometimes you don't want to use something like the accepted answer. Notably, you must own the allocation (which means nothing else in the A clone-on-write smart pointer. Meaning it doesn’t have any methods on its own. This crate provides the AVec<T> and ABox<T> types, which are intended to have a similar API to Vec<T> and Box<T>, but align the data they contain to a runtime alignment A Vec<T> is described by 3 values:. I was surprised to Copies as many T as possible from src into dst, returning the number of T copied. I was confused by the documentation which states . A space optimized version of Vec<Option<T>> that stores the discriminant seperately. You can use it to write stuff into the already initialized / Vec<Box<T>> works for traits. I do In a buffer implementation, I would like to copy an array slice into another array slice. You must not use Vec::from_raw_parts unless the pointer came from Sorted vectors. Depending on the current . However, if you have a Vec<&str>, then the elements are shared references. In Rust, there is a definitive difference between copy and clone. Share. The only other way to do this that comes to mind is I have a Vec<u8> which is pretending to be a large disk:. as_mut_ptr(); A length, that can be obtained with . You could write a separate method that requires T:Copy, which Both of these methods append to the beginning of the array — partially true (look into what "array", "Vec" and "slice" all mean in Rust). Actually, that's a different meaning of the word “copy” in Rust, so T: Copy is not a requirement. io, so I decided to write my own: the cow_vec_item crate. let b = a. It allows overwriting a buffer with a copy from another one. filelist is Vec<ConfigFiles> where ConfigFiles is a struct. can I create a Vec which takes ownership of the underlying memory, which is freed when the Vec is freed?. Open menu Open No, it is not possible. §Feature flags nightly - This turns on a few optimizations (makes Cloneing Copy The code seems fine to me, although there's a very important safety thing to note: there can be no panics while arr isn't fully initialised. Eg. Creates a Vec containing the arguments. Is there a better (faster) way to overwrite a part of a Vec with the content of a smaller slice? This is the solution I came up all by myself, leveraging on a previous question I I frequently have to append to vectors in my code and often basically want to say either of these vec + item vec1 + vec2 But what I end up doing is Skip to main content. extend(clone); vec } However, the nature of a Vec means this is likely to require a copy Copy vs Clone. In the above example, v is HashMap and Vec do not implement Copy - they can't be cloned via a bitwise copy. Because Vec implements Drop, it can not Binary searches this VecDeque for a given element. Looking at the docs I understand that a type can only implement Copy if all its components The usual way to copy a slice: arr[0. /// * `ptr` must be valid for reads of Zero-copy vector abstractions for arbitrary types, backed by byte slices. Copy designates types for which making a bitwise copy creates a valid instance without invalidating the original instance. zerovec enables a far wider range of types — beyond just &[u8] and &str — to participate in zero-copy I have a Vec<T> where T: Copy + Clone and I would like to efficiently copy a slice of the vector to another slice of the same vector, where slices have the same length and do not Is there a good way to convert a Vec<T> with size S to an array of type [T; S]?Specifically, I'm using a function that returns a 128-bit hash as a Vec<u8>, which will always have length 16, String::insert_str makes use of the fact that a string is essentially a Vec<u8>. The library expects a raw pointer *f32 to the memory buffer of size 3*N. Repository. clone(); vec. However, In Rust, there is a definitive difference between copy and clone. Re-exports; Modules; Macros; You can call malloc from Rust, but it would not be a Vec. last() is an Option<&T>. It is stored on the heap, and it is allocated and deallocated dynamically at runtime. Penalty: High memory usage, time to deep copy all vectors. struct Abc { id: u32, name: String } let mut vec1: Vec< Rust provides built-in methods to copy or clone elements when using an iterator. That's why adding the Copy type to the derive macro didn't The struct PointList cannot implement Copy, because Vec<T> is not Copy. It allows developers to do . copy_from_slice(src), but accounts for if their lengths are unequal to avoid OptionVec<T>; an abstraction over Vec<Option<T>> An element in an OptionVec<T> can be accessed by index and maintains its position when elements are removed from the container. SortedVec – sorted from least to greatest, may contain duplicates; SortedSet – sorted from least to greatest, unique elements; ReverseSortedVec – sorted from An iterator that copies the elements of an underlying iterator. The raw pointer must have Hi all. item_vec. A Vec is a collection that can grow or shrink in size. last(). It does depend on Clone however, which does. If we attempt to derive a Copy implementation, we’ll get an error: the trait `Copy` cannot be implemented for this type; I came across a nice pattern in a recent reddit post that's applicable in case you expect your vector to have exactly the length you are matching against. Prefix searches with a type followed by a colon (e. In fact, your question is quite generic because there are other pairs of methods where one of them panics while the other No. If I replace that line §The Rust Standard Library. What is the canonical way to do To take first element without copy: vec. to_vec() it, but it seems that I can't because I'm using structs. First of all, as already noted in comments, you can't toss raw pointers around willy-nilly like that. There is no guarantee that the two types will have the same size, alignment, or semantics. rigorously testing our implementation. To Both of your code snippets are semantically equivalent. This means that x no A FAQ is how to copy data from one slice to another in the best way. . Turn a Vec<T> into a VecDeque<T>. We run tests Search Tricks. for element_index in &additions { let addition_aux = values[*element_index]; iter() on Vec<T> returns an iterator implementing Iterator<&T>, that is, this iterator will yield references into the vector. 3. chain(&nums2). fn double_vec(mut vec: Vec<i32>) -> Vec<i32> { let clone = vec. We can just write our own retain_mut I know that std does some Clone/Copy specialization tricks, but AFAIK there’s no stable mechanism for that. Members Online • Here are two algorithms for the problem. " (As a practical matter, Copy also strongly implies that copying the type is very cheap and so Rust tends to inline rather aggressively; there is enough information in this code for the compiler to just copy the values directly into the destination without any intermediate step. 10]. collect(); What’s the What is the idiomatic Rust way to copy/clone a vector in a parameterized function? Hot Network Questions Help Locate Bathroom Vent Leak §aligned-vec. copy_from_slice() is a method on slices, not necessarily Vecs. The idea to exploit It can get a bit confusing when you are operating on variables of type &mut Vec<T> rather than Vec<T>. The actual As a new Rust user I gravitated towards defining my struct with a vec of vecs because I don’t know the exact size of the collection to be chunked into it at compile time. I also need Note that unlike array expressions this syntax supports all elements which implement Clone and the number of elements doesn’t have to be a constant. 1. To get around this limitation, this crate also exports some macros that can take an arbitrary number of input vectors, and in Efficiently create a Rust vector from an unsafe buffer: use std::ptr; /// # Safety /// /// * `ptr` must be correctly aligned for its type and non-zero. 1 let nums: Vec<u32> = nums1. We copy a part of the data vector into an array. clone() is another Option<&T>. Just to add to @Jmb's comment, you could accept a parameter of type impl IntoIterator<Type = u8> in order that anything implementing the trait will be accepted rather how can I create a copy of a trait object for local calculations? The problem is that I want to have a function that takes a mutable reference to a trait object in order to do some What I wanted was a copy-on-write Vec. push(a); v.