Closed
Description
Rust 1.47.0-stable and 1.50.0-nightly (2020-11-18 8256379832b5ecb7f71e), both tested on the playground.
trait Example {
type Ty;
}
impl<'a> Example for &'a i32 {
type Ty = &'a i32;
}
fn example<F: Fn(<&i32 as Example>::Ty)>(f: F) { }
fn main() {
example(&|i: &i32| println!("{}", *i));
example(|i: &i32| println!("{}", *i));
fn print_integer(i: &i32) { println!("{}", *i); }
example(&print_integer);
example(*&print_integer); //fails
example(print_integer); //fails
}The first three calls to example succeed, but the last two calls fail with this error:
error[E0631]: type mismatch in function arguments
--> src/main.rs:18:13
|
9 | fn example<F: Fn(<&i32 as Example>::Ty)>(f: F) { }
| ------------------------- required by this bound in `example`
...
15 | fn print_integer(i: &i32) { println!("{}", *i); }
| ------------------------- found signature of `for<'r> fn(&'r i32) -> _`
...
18 | example(print_integer); //fails
|
#76956 may be related.
The error does not occur if...
- The
Fn(<&i32 as Example>::Ty)bound is replaced withFn(&i32) - All occurrences of
&i32are replaced withi32 - The
examplefunction is given a lifetime parameter which is otherwise ignored:
fn example<'a, F: Fn(<&'a i32 as Example>::Ty)>(f: F) { }
- The generic lifetime is replaced with a generic type:
trait Example {
type Ty;
}
impl<T> Example for Vec<T> {
type Ty = Vec<T>;
}
fn example<F: Fn(<Vec<u8> as Example>::Ty)>(f: F) { }
fn main() {
example(&|v: Vec<u8>| println!("{:?}", v));
example(|v: Vec<u8>| println!("{:?}", v));
fn print_bytes(v: Vec<u8>) { println!("{:?}", v); }
example(&print_bytes);
example(*&print_bytes);
example(print_bytes);
}Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment