Borrowed value does not live long enough requiring static lifetime - rust

Question

I'm getting this error with a sample code at this rust playground
Compiling playground v0.0.1 (/playground)
error[E0597]: `text` does not live long enough
--> src/main.rs:34:38
|
34 | let item = NotLongEnough { text: &text };
| ^^^^^ borrowed value does not live long enough
35 | let mut wrapper = Container { buf: Vec::new() };
36 | wrapper.add(Box::new(item));
| -------------- cast requires that `text` is borrowed for `'static`
...
40 | }
| - `text` dropped here while still borrowed
error: aborting due to previous error
For more information about this error, try `rustc --explain E0597`.
error: could not compile `playground`
To learn more, run the command again with --verbose.
The contents are:
trait TestTrait {
fn get_text(&self) -> &str;
}
#[derive(Copy, Clone)]
struct NotLongEnough<'a> {
text: &'a str,
}
impl<'a> TestTrait for NotLongEnough<'a> {
fn get_text(&self) -> &str {
self.text
}
}
struct Container {
buf: Vec<Box<dyn TestTrait>>,
}
impl Container {
pub fn add(&mut self, item: Box<dyn TestTrait>) {
self.buf.push(item);
}
pub fn output(&self) {
for item in &self.buf {
println!("{}", item.get_text());
}
}
}
fn main() -> Result<(), Box<dyn std::error::Error>> {
let text = "test".to_owned();
let item = NotLongEnough { text: &text };
let mut wrapper = Container { buf: Vec::new() };
wrapper.add(Box::new(item));
wrapper.output();
Ok(())
}
I have no clue why cast requires that text is borrowed for 'static
Could someone please help me with this? I've no idea what I've done wrong.

Answer 1

TLDR: Fixed version
The problem is in your Container definition:
struct Container {
buf: Vec<Box<dyn TestTrait>>,
}
The statement dyn TestTrait is equivalent to dyn TestTrait + 'static, meaning that your trait objects must not contain any references with lifetime less than 'static.
In order to fix the problem, you have to replace that trait bound with a less strict one:
struct Container<'a> {
buf: Vec<Box<dyn TestTrait + 'a>>,
}
Now instead of 'static, the container requires 'a. And you have to apply that change to the implementation as well:
pub fn add(&mut self, item: Box<dyn TestTrait + 'a>) { // notice the new trait-bound
self.buf.push(item);
}
Relevant resources:
Trait bounds