Newtype (usize) efficacy and idiomatic usage

help
1

I have a newtype

#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Hash)]
// Type wrapper for Author IDs
pub struct AuthorId(usize);

It works. Using it produces good results. Fixing various compiler errros (very clear messages from the compiler), I wondered about one aspect.
In a lot of places, when I have an aid of type AuthorId, and am passing it around, I need to ssay aid.clone() to tell the compiler I want a copy of the value.
As I understand it, if I were just using a usize, the compiler would do this automatically.
I think I could get the compiler to do this automatically for AuthorId by deriving Copy for it?
If so, is that a good idea, or is it more maintainable to have the explicit clone() calls?
Thanks,
Joel

2

In this case, because the contents are Copy, there is no drawback to deriving Copy for the newtype and this is standard practice.

3

The only reasons to refrain from derive(Copy) or impl Copy for AuthorId, would be if one of these special cases applied:

  • You expect that in the future, AuthorId will be unable to implement Copy (e.g. due to containing a string). Then, using Copy now would be something you have to take out later.
  • The number of copies is meaningful and you want to make it explicit when a copy is made, or take an action then.

But neither of those are plausible for an ID number type, so do it.

4

Thanks for the quick replies. I will switch to using Copy.