Closed as not planned
Description
Code
I tried this code:
use std::any::Any;
// Generic trait used to store multiple different kinds of objects dynamically
trait Foo<T> : Any {
fn as_any(&self) -> &dyn Any;
}
// Example (empty) implementation of the Foo trait
// The error is not related to this structure, it is only needed to have a meaningful example in the main function
#[derive(Copy, Clone, Debug)]
struct FooImpl;
impl Foo<usize> for FooImpl {
fn as_any(&self) -> &dyn Any {
self
}
}
// Finds all instances of type F in the array of Foo trait objects
fn find<T, F : Foo<T> + Clone>(vec: &Vec<Box<dyn Foo<T>>>) -> Vec<F> {
vec.iter()
.filter_map(|foo| foo.as_ref().as_any().downcast_ref::<F>())
.cloned()
.collect()
}
fn main() {
let mut vec: Vec<Box<dyn Foo<usize>>> = Default::default();
vec.push(Box::new(FooImpl));
// "find all instances of FooImpl in vec"
let result = find::<usize, FooImpl>(&vec);
println!("Results: {:?}", result);
}I expected to see this happen: code compiles
Instead, this happened: code doesn't compile (see error below)
Version it worked on
It most recently worked on toolchain 1.60-x86_64-unknown-linux-gnu
rustup run 1.60-x86_64-unknown-linux-gnu rustc --version --verbose:
rustc 1.60.0 (7737e0b5c 2022-04-04)
binary: rustc
commit-hash: 7737e0b5c4103216d6fd8cf941b7ab9bdbaace7c
commit-date: 2022-04-04
host: x86_64-unknown-linux-gnu
release: 1.60.0
LLVM version: 14.0.0
Version with regression
rustc --version --verbose:
rustc 1.62.1 (e092d0b6b 2022-07-16)
binary: rustc
commit-hash: e092d0b6b43f2de967af0887873151bb1c0b18d3
commit-date: 2022-07-16
host: x86_64-unknown-linux-gnu
release: 1.62.1
LLVM version: 14.0.5
Backtrace
Compilation error on stable
$ cargo build
Compiling test-annotation v0.1.0 ([REDACTED]/test-annotation)
error[E0310]: the parameter type `T` may not live long enough
--> src/main.rs:18:40
|
18 | .filter_map(|foo| foo.as_ref().as_any().downcast_ref::<F>())
| ^^^^^^ ...so that the type `dyn Foo<T>` will meet its required lifetime bounds...
|
note: ...that is required by this bound
--> src/main.rs:3:16
|
3 | trait Foo<T> : Any {
| ^^^
help: consider adding an explicit lifetime bound...
|
16 | fn find<T: 'static, F : Foo<T> + Clone>(vec: &Vec<Box<dyn Foo<T>>>) -> Vec<F> {
| +++++++++
For more information about this error, try `rustc --explain E0310`.
error: could not compile `test-annotation` due to previous error