Error code E0049

An attempted implementation of a trait method has the wrong number of type or const parameters.

Erroneous code example:

#![allow(unused)] fn main() { 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:

#![allow(unused)] fn main() { trait Foo { fn foo<T: Default>(x: T) -> Self; } struct Bar; impl Foo for Bar { fn foo<T: Default>(x: T) -> Self { // ok! Bar } } }