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# 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
        }
    }
    }