Type aliases and new types are two subtly different features. The new type pattern allows you to provide new impls for the underlying type (it is a new type af

Type aliases and new types are two subtly different features. The new type pattern allows you to provide new impls for the underlying type (it is a new type after all) while the type alias is pure sugar where type T = U allows the string T to be substituted for U in any place where T is imported. If U is a foreign type you cannot provide new trait impls for it.