Both approaches are useful at different times. For example you wouldn't want to accidentally multiple a meter by a centimeter but you may want to provide std::i

Both approaches are useful at different times. For example you wouldn't want to accidentally multiple a meter by a centimeter but you may want to provide std::io::Result<T> which is equivalent to Result<T, std::io::Error> but just a bit nicer to type. For example in Rust you can do: type Foo = Bar; Which is just an alias, interchangeable with Bar. Or you can do: struct Foo(Bar); Which is a completely new type that just so happens to contain a Bar.