For questions related to Trait Objects (dynamically-dispatched objects) in Rust
Trait objects are the dynamically dispatched objects in Rust. They are unsized, so they are used behind some kind of reference (Box, for example).
Questions tagged [trait-objects]
183 questions
2
votes
1 answer
How to make type-erased version of a trait with associated type?
Say there is a collection trait that has an associated type for its items:
trait CollectionItem {
// ...
}
trait Collection {
type Item: CollectionItem;
fn get(&self, index: usize) -> Self::Item;
// ...
}
Can I somehow…
Heinzi
- 5,793
- 4
- 40
- 69
2
votes
1 answer
How can I avoid consuming a value passed to an `impl Trait` parameter?
How can I keep ownership of a value after passing it to a function that takes a impl Trait as a parameter? I've tried both passing the parameter as a reference and without the & but none of them worked.
trait Noise{
fn make_noise(&self);
fn…
EscFox
- 23
- 3
2
votes
0 answers
Problem with trait object storing its reference elsewhere
I want to have a method to_holder of SomeTrait that'll store reference to the trait object to a struct, but the compiler forces Self of method to_holder to be Sized. Annotating Self: Sized does work, but that way I can't call to_holder from a trait…
danzou1ge6
- 53
- 2
2
votes
1 answer
rust generic type with trait bound when use trait objects
trait MyTrait {
fn my_f(&self) ;
}
struct A {}
struct B {}
impl MyTrait for A {
fn my_f(&self) {
println!("A.my_f()");
}
}
impl MyTrait for B {
fn my_f(&self) {
println!("B.my_f()");
}
}
struct MyList
Matt.Z
- 602
- 7
- 19
2
votes
2 answers
Why can't Box be pased to a function with &mut Trait as parameter
I'm sure this has been asked previously but haven't encountered a question that captures the precise scenario here. I have the following code:
let mut pool: Box = <...>
redis::cmd(COMMAND)
.arg(LIST)
…
rumdrums
- 1,322
- 2
- 11
- 25
2
votes
1 answer
Is it possible (in any way) to pass a trait object to a generic method?
I have a boxed trait object; I was wondering if, in any way, this can be passed to a method with a generic type bound:
trait Trait {
fn tmethod(&self) {
println!("hello");
}
}
impl Trait for Vec {}
fn call_tmethod(t:…
Marcus
- 5,104
- 2
- 28
- 24
2
votes
1 answer
Can Clone be implemented for a trait object with finite lifetime (without using unsafe code)?
First things first: What am I trying to achieve?
I'm trying to use Iterator::fold() with an accumulator that itself is an Iterator, but in addition I need a clone of that iterator internally.
fn whatever(some_iterator : T,…
soulsource
- 197
- 7
2
votes
1 answer
Incorrect type inference for Rust vector of trait object
I am having trouble understanding the following error:
// test.rs
struct A {
a: u32
}
trait B { }
impl B for A { }
struct C {
c: Vec>,
}
fn test() {
let a = A {a: 1};
let a_vec = vec![Box::new(a)];
let c = C {
…
Jason Qiu
- 23
- 3
2
votes
1 answer
Using generics, trait aliases, and constructors in Rust
Context
I have a DataStore trait that abstracts out data storage. (For example, I can create a simple implementation of this trait for data stores that wrap Vecs and HashMaps.) I would like this abstraction because some use cases/targets…
Chris Swierczewski
- 679
- 6
- 24
2
votes
2 answers
How to create Vec of references to generic trait objects in Rust?
I am new to Rust. My background is Java. I am trying to solve the following problem.
I have a trait Fuel which is implemented for struct Diesel and struct Gas.
I also have a trait Vehicle with Fuel generic type parameter. Vehicle is implemented for…
Vadim
- 576
- 1
- 4
- 13
2
votes
2 answers
How can I store a closure object in a struct?
I can't figure out how to store a closure object in a struct. The arguments and return for the closure object are known. Here's my condensed code:
struct Instr
where F: Fn([i32;4],[i32;3]) -> [i32;4]
{
name: String,
op: F
}
fn…
Tumbleweed53
- 1,491
- 7
- 13
2
votes
1 answer
How to convert an `Arc` into an `Arc`?
I have a library that needs things to implement a specific trait (TQDispatch).
In my main project I have a vector of objects that all implement a different trait (Device) which I need for dynamic dispatch.
The device trait is declared
pub trait…
pm100
- 48,078
- 23
- 82
- 145
2
votes
1 answer
How do I pass in a trait object to a vector that will also have a uniform type in the vector of the vector?
This is really hard to explain concisely. But what I want is a struct that has a field of Vec "A" containing a vector of threads with another Vec "B" inside the Vec "A". Vec "A" holds both the Vec "B" and thread handle. Vec "B" has a uniform type,…
entropy32
- 169
- 3
- 11
2
votes
2 answers
Cast Arc> to Arc
I am writing a graph implementation with edges and nodes. The graph should be accessed concurrently so I chose to build the Edges and Nodes as Arc> and Arc>.
Unfortunately I get a compile error the parameter type 'T'…
CoronA
- 7,717
- 2
- 26
- 53
2
votes
2 answers
How to pass a closure via dynamic dispatch in an object-safe method?
How do you pass a closure to an object-safe trait method or otherwise via dynamic dispatch?
I have answered this myself, but the answer leaves something wanting: FnOnce closures must be boxed since they are not sized and must be consumed on use…
dhardy
- 11,175
- 7
- 38
- 46