# Error code E0322

A built-in trait was implemented explicitly. All implementations of the trait are provided automatically by the compiler.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    struct Foo;

    impl Sized for Foo {} // error!
    }

The `Sized` trait is a special trait built-in to the compiler for types with a constant size known at compile-time. This trait is automatically implemented for types as needed by the compiler, and it is currently disallowed to explicitly implement it for a type.