Error code E0223
An attempt was made to retrieve an associated type, but the type was ambiguous.
Erroneous code example:
trait Trait { type X; }
fn main() {
let foo: Trait::X;
}
ⓘ
The problem here is that we're attempting to take the associated type of X
from Trait
. Unfortunately, the type of X
is not defined, because it's only
made concrete in implementations of the trait. A working version of this code
might look like:
trait Trait { type X; }
struct Struct;
impl Trait for Struct {
type X = u32;
}
fn main() {
let foo: <Struct as Trait>::X;
}
This syntax specifies that we want the associated type X
from Struct
's
implementation of Trait
.
Due to internal limitations of the current compiler implementation we cannot
simply use Struct::X
.