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
1
vote
0 answers
How do I use a trait object in a BinaryHeap?
I have the following simplified code:
use std::collections::BinaryHeap;
use std::rc::Rc;
struct JobId;
struct Coord;
struct TimeStep;
pub trait HasJob {
fn id(&self) -> JobId;
fn start(&self) -> Coord;
fn end(&self) -> Coord;
fn…
shadeMe
- 706
- 1
- 10
- 30
1
vote
1 answer
Create Read trait object from u8 slice
I'm trying to create a Read trait object from a u8 slice, to use in murmur3 crate, like this
fn main() {
let mut arr: [u8; 4] = [1, 2, 3, 4];
let mut slice: &mut [u8] = &mut arr;
let mut read: &mut std::io::Read = &mut slice;
}
But I…
Mikhail Cheshkov
- 226
- 2
- 14
1
vote
0 answers
How can I cast Rc to Rc>>
I have a trait MyTrait and a struct MyStruct that implements MyTrait.
I also have a function that accepts Rc>> as an argument.
Somewhere in the code I create an instance of Rc>>:
let my_struct =…
Dmitry Uvarov
- 673
- 6
- 6
0
votes
1 answer
Problem with returning generic type from function
I have a function that searches through a list of trait objects and attempts to find one whose implementor is of a specific type, however the compiler doesent accept the return type.
pub struct GameObject{
pub modules: Vec>,…
Isaksak
- 3
- 1
0
votes
1 answer
Blanket `impl Trait1` for all types which `impl Trait2` and functions which return `impl Trait2`
I want to implement HasChildren for all types which implement Element and for all functions which return impl Element.
My case use is that I have a Vec> in which I want to be able to store both types which implement Element and…
Max888
- 3,089
- 24
- 55
0
votes
2 answers
Rust impl multiple times both for struct and traits
Think below code, impl multiple times both for struct and traits:
mod m {
pub trait Foo {
fn xyzzy(&self) { println!("foo!"); }
}
pub trait Bar {
fn xyzzy(&self) { println!("bar!"); }
}
pub trait Quux:…
James Yang
- 476
- 5
- 6
0
votes
1 answer
Getting a slice of trait objects from a slice of an associated type
I have two related traits List and ListItem (playground link).
trait List {
type Item: ListItem;
fn items(&self) -> Vec;
/* more stuff */
}
where Item is an associated type on List and ListItem has a custom implementation…
Increasingly Idiotic
- 5,700
- 5
- 35
- 73
0
votes
1 answer
Is there a way to implement trait objects with generic functions?
Basically I am trying to implement visitors-coding paradigm, where Expr trait needs to be implemented by Binary struct. I want to use Expr as a trait object. Any entity wanting to interact with Expr will need to implement Visitors trait. The visitor…
Adnan
- 88
- 1
- 7
0
votes
1 answer
Storing an iterator over borrowed refs inside a Struct
I'm new to Rust and like many finding lifetimes quite hard to get the hang of. I get the basics, but I can't quite fathom how to make this work.
I'm trying to implement an abstract data structure that holds a collection of records. One requirement…
d11wtq
- 34,788
- 19
- 120
- 195
0
votes
1 answer
What happens when I pass a concrete struct reference to a function that takes trait objects?
In the following code I have a simple trait, A, and a struct Foo that implements A...
Next, I define a function that takes a reference to a trait object. From main() I pass in a reference to a concrete Foo. This works fine and successfully calls the…
Chuck
- 1,850
- 2
- 17
- 28
0
votes
1 answer
How can I avoid allocation when filtering on a set of items with a higher order function?
Trying to filter a set of items, based on a predicate that is generic, because computed at run-time:
fn main () {
let el = vec![
vec![10, 20, 30],
vec![40, 50, 60]
];
println!("{:?}", use_predicate(el,…
doplumi
- 2,938
- 4
- 29
- 45
0
votes
1 answer
Trait objects force higher-ranked trait bounds, which break nested closures
I am in a situation where Rust makes me add a HRTB for a generic type that is used as argument in a trait object. But this HRTB makes nested closures not work.
Here's the trait I'm going to use to make a trait object Box:
trait OpTrait…
Kurt Schelfthout
- 8,880
- 1
- 30
- 48
0
votes
2 answers
Trait object as associated type of a trait object
I wrote two structs that implement a common trait Solve. Solve has an associated type Answer with trait bound Display. I want the function create_solver to return a trait object of Solve.
I need help with writing the associate type Answer = ??.
use…
stackcycle
- 3
- 1
0
votes
2 answers
Clone custom structs of concrete type as trait objects
Using Rc, I can cast an Rc of a concrete type to a trait object:
use std::rc::Rc;
trait Foo {}
impl Foo for usize {}
fn main() {
let x: Rc = Rc::new(1);
let y: Rc = x.clone();
}
Playground.
If I define a wrapper for an Rc…
Román Cárdenas
- 492
- 5
- 15
0
votes
0 answers
Filter vec of trait objects by other trait and return all trait objects that implement given trait
I'm trying to filter a vec of trait objects by a trait and return a subset of the vec which contains all objects that implement given trait, similar to Bevys Query<>.
I came up with this:
pub fn filter<'a, T: Entity + Sized>(vector: &'a mut…
Joffi
- 16
- 2