Is there a heapless trait object? - rust

Question

Is there a way to implement trait objects completely in stack memory?
This is the code that I use Box and thus heap memory:
extern crate alloc;
use alloc::vec::Vec;
use alloc::boxed::Box;
pub trait ConnectionImp {
fn send_data(&self);
}
pub struct Collector {
pub connections: Vec<Box<dyn ConnectionImp>>
}
impl Collector {
pub fn new() -> Collector {
Collector {
connections: Vec::with_capacity(5),
}
}
pub fn add_connection(&mut self,conn: Box<dyn ConnectionImp> ){
self.connections.push(conn);
}
}
I tried to use heapless crate but I could not find any replacement for Box. The following code shows the result of my effort:
use heapless::{Vec,/*pool::Box*/};
extern crate alloc;
use alloc::boxed::Box;
pub trait ConnectionImp {
fn send_data(&self);
}
pub struct Collector {
pub connections: Vec<Box<dyn ConnectionImp>,5>
}
impl Collector {
pub fn new() -> Collector {
Collector {
connections: Vec::new(),
}
}
pub fn add_connection(&mut self, conn: Box<dyn ConnectionImp> ){
self.connections.push(conn);
}
}

Answer 1

Yes, you can use &dyn Trait. A lot of examples of dynamic dispatch use Box because it's a more common use-case and using references introduces lifetimes, which tend to make examples more complicated.
Your code would become:
pub struct Collector<'a> {
pub connections: Vec<&'a dyn ConnectionImp>,
}
impl<'a> Collector<'a> {
pub fn new() -> Collector<'a> {
Collector {
connections: Vec::new(),
}
}
pub fn add_connection(&mut self, conn: &'a dyn ConnectionImp) {
self.connections.push(conn);
}
}