The point of a newtype is that it allows you to create a wrapper around some other type for one of the following two purposes:
1. Marking the kind of data to prevent mixing up values of different kinds. (e.g. Email)
2. Outlawing some of the values of the underlying type. (e.g. OneToFive)
I do not think it being a tuple-struct or not is important at all when deciding whether something uses the newtype pattern, as long as it has a single field.
Re:Names are not type safety
by steveklabnik on Monday November 02, 2020 @10:38AM
(#24969239)
Do you feel that just because the inner value is named, rather than unnamed, it’s no longer a new type? Trying to figure out what line is crossed here.
Re:Names are not type safety
by chrisoverzero on Monday November 02, 2020 @12:32PM
(#24970677)
I'm going by the Rust documentation: https://doc.rust-lang.org/stable/rust-by-example/generics/ne...
(I was going to be cheeky here, but Git history shows you didn't write any of this part.)
Re:Names are not type safety
by steveklabnik on Monday November 02, 2020 @03:05PM
(#24972551)
Hehe yeah, I mean, I am not 100% sure myself, which is why I asked.
There's no real difference between a 1-tuple struct and the regular struct, other than the name. So to me, it feels like either are both newtypes. But, I guess I could see some sort of argument the other way too.
Re:Names are not type safety
by lexi-lambda on Monday November 02, 2020 @05:38PM
(#24974307)
In Haskell, a newtype can be a single-field record with a named field, so from a Haskell perspective, I would definitely consider both of them “newtypes.”
It is not. `NonZeroUsize` is (though in Rust "newtype" is only a pattern or idiom), and its definition (inside of a macro which provides numeric newtypes a bunch of `impl`s) is:
But here's String: …which is a normal `struct` _containing_ a named `Vec<u8>`. Of the types you mentioned, only `NonZeroUsize` conforms to the pattern.