I'm trying to implement an EventListener like interface in rust. I have a trait that takes a callback, the callback should mutate a variable from the scope it was defined in. But I get an error saying the borrowed value does not live long enough.
pub struct Target<T> {
funcs: Vec<Box<dyn FnMut(T) -> ()>>,
}
impl<T: Clone + 'static> Target<T> {
pub fn new() -> Target<T> {
return Target { funcs: Vec::new() };
}
pub fn add_listener(&mut self, func: Box<dyn FnMut(T) -> ()>) -> () {
self.funcs.push(Box::new(func));
}
pub fn trigger(&mut self, x: T) {
for callback in &mut self.funcs {
callback(x.clone());
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn trigger_mutation() {
let mut a = 0;
let mut t: Target<i32> = Target::new();
t.add_listener(Box::new(|x: i32| {
println!("{}", x);
a = x;
}));
t.trigger(42);
let b = a.clone();
assert_eq!(b, 42);
}
}
I run it and get this:
$ cargo test -- --nocapture
Compiling luma-connector v0.1.0 (/home/blake/git/connector)
error[E0597]: `a` does not live long enough
--> src/target.rs:32:13
|
30 | t.add_listener(Box::new(|x: i32| {
| - -------- value captured here
| ________________________|
| |
31 | | println!("{}", x);
32 | | a = x + 1;
| | ^ borrowed value does not live long enough
33 | | }));
| |__________- cast requires that `a` is borrowed for `'static`
...
37 | }
| - `a` dropped here while still borrowed
