Error code E0119

There are conflicting trait implementations for the same type.

Erroneous code example:

#![allow(unused)] fn main() { trait MyTrait { fn get(&self) -> usize; } impl<T> MyTrait for T { fn get(&self) -> usize { 0 } } struct Foo { value: usize } impl MyTrait for Foo { // error: conflicting implementations of trait // `MyTrait` for type `Foo` fn get(&self) -> usize { self.value } } }

When looking for the implementation for the trait, the compiler finds both the impl<T> MyTrait for T where T is all types and the impl MyTrait for Foo. Since a trait cannot be implemented multiple times, this is an error. So, when you write:

#![allow(unused)] fn main() { trait MyTrait { fn get(&self) -> usize; } impl<T> MyTrait for T { fn get(&self) -> usize { 0 } } }

This makes the trait implemented on all types in the scope. So if you try to implement it on another one after that, the implementations will conflict. Example:

trait MyTrait { fn get(&self) -> usize; } impl<T> MyTrait for T { fn get(&self) -> usize { 0 } } struct Foo; fn main() { let f = Foo; f.get(); // the trait is implemented so we can use it }