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
.