Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0212: cannot use the associated type of a trait with uninferred generic parameters
What it meansCannot use the associated type of a trait with uninferred generic parameters.
What rustc prints
error[E0212]: cannot use the associated type of a trait with uninferred generic parameters --> main.rs:8:12 | 8 | field: I::A) {} // error! | ^^^^ | help: use a fully qualified path with inferred lifetimes | 8 - field: I::A) {} // error! 8 + field: <I as Foo<&isize>>::A) {} // error! |
Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
E0212Types and traits
Activein rustc 1.99.0
8related errors linked below
The compiler team's explanation
Cannot use the associated type of a trait with uninferred generic parameters.
Erroneous code example:
pub trait Foo<T> {
type A;
fn get(&self, t: T) -> Self::A;
}
fn foo2<I : for<'x> Foo<&'x isize>>(
field: I::A) {} // error!In this example, we have to instantiate 'x, and we don't know what lifetime to instantiate it with. To fix this, spell out the precise lifetimes involved. Example:
pub trait Foo<T> {
type A;
fn get(&self, t: T) -> Self::A;
}
fn foo3<I : for<'x> Foo<&'x isize>>(
x: <I as Foo<&isize>>::A) {} // ok!
fn foo4<'a, I : for<'x> Foo<&'x isize>>(
x: <I as Foo<&'a isize>>::A) {} // ok!From rustc --explain E0212 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0308mismatched types
- E0277the trait bound is not satisfied
- E0599no method named X found in the current scope
- E0433failed to resolve
- E0206the trait `Copy` cannot be implemented for this type
- E0210This error indicates a violation of one of Rust's orphan rules for trait implementations. The rule concerns the use of type parameters in an implementation of a foreign trait (a trait defined in another crate), and states that type parameters must be "covered" by a local type
- E0214parenthesized type parameters may only be used with a `Fn` trait
- E0220associated type `Baz` not found for `Self`
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?