Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0049: associated function `foo` has 0 type parameters but its trait declaration has 1 type parameter
What it meansAn attempted implementation of a trait method has the wrong number of type or const parameters.
What rustc prints
error[E0049]: associated function `foo` has 0 type parameters but its trait declaration has 1 type parameter
--> main.rs:10:11
|
2 | fn foo<T: Default>(x: T) -> Self;
| - expected 1 type parameter
...
10 | fn foo(x: bool) -> Self { Bar }
| ^ found 0 type parametersReal 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.
The compiler team's explanation
An attempted implementation of a trait method has the wrong number of type or const parameters.
Erroneous code example:
trait Foo {
fn foo<T: Default>(x: T) -> Self;
}
struct Bar;
// error: method `foo` has 0 type parameters but its trait declaration has 1
// type parameter
impl Foo for Bar {
fn foo(x: bool) -> Self { Bar }
}For example, the Foo trait has a method foo with a type parameter T, but the implementation of foo for the type Bar is missing this parameter. To fix this error, they must have the same type parameters:
trait Foo {
fn foo<T: Default>(x: T) -> Self;
}
struct Bar;
impl Foo for Bar {
fn foo<T: Default>(x: T) -> Self { // ok!
Bar
}
}From rustc --explain E0049 (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
- E0044foreign items may not have type parameters
- E0046not all trait items implemented, missing: `foo`
- E0050method `foo` has 1 parameter but the declaration in trait `Foo::foo` has 2
- E0053method `foo` has an incompatible type for trait
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?