Understanding Rust Error E0407

Rust Error E0407: Method Not in the Implemented Trait

Rust Error E0407 occurs when a method is defined in a trait implementation but this method is not part of the trait being implemented. This often happens if there is a typo in the method name, or the method is placed in the wrong implementation block.

Erroneous code example:

#![allow(unused)]
fn main() {
trait Foo {
    fn a();
}

struct Bar;

impl Foo for Bar {
    fn a() {}
    fn b() {} // error: method `b` is not a member of trait `Foo`
}
}

Solution

To fix Rust Error E0407, verify that the method name is spelled correctly and is part of the correct trait. Another possibility is to move the method to another appropriate implementation block or define it in the trait declaration. Here are a couple of corrected examples:

First example:

#![allow(unused)]
fn main() {
trait Foo {
    fn a();
    fn b();
}

struct Bar;

impl Foo for Bar {
    fn a() {}
    fn b() {} // ok!
}
}

Second example:

#![allow(unused)]
fn main() {
trait Foo {
    fn a();
}

struct Bar;

impl Foo for Bar {
    fn a() {}
}

impl Bar {
    fn b() {}
}
}

Conclusion

Rust Error E0407 is caused by defining a method in a trait implementation that is not part of the trait being implemented. To fix this error, ensure the method name is accurate and is included in the appropriate trait or implementation block.