Add NewType by ilevkivskyi · Pull Request #226 · python/typing (original) (raw)

I could not follow anything from the Scala ValueType description (no news
there :-).

The explanation "it is the same type with a different name" feels wrong --
if it really was the same name it would be a type alias. In fact it is not
the same type, it has a specific relationship to the original type, which
is exactly that it is a subtype (but not every subtype is a NewType).

I will check with Jukka but unless he has strong objections I am going for
Distinct Type (two words) when we're discussing it in English text, but I
will keep NewType (one function) in code.

On Wed, Jun 1, 2016 at 1:42 AM, Sietse Brouwer notifications@github.com
wrote:

I like @lgautier https://github.com/lgautier's NamedType a lot: to me,
it expresses "this is otherwise the same type, but it has a different name
(and therefore its own meaning)". Also, like he says, it meshes nicely with
namedtuple (and typing.NamedTuple).

How I would read it:

UserID = NamedType('UserID', int) -> This is a type of int named UserID

---

If NamedType does not make it, what about ValueType?

• ValueType: Scala has the same concept, and calls them Value Classes
  http://docs.scala-lang.org/overviews/core/value-classes.html. It
  expresses nicely that this type does not say something about the data
  structure, but about the value it contains.

How I would read it:

UserID = ValueType('UserID', int) -> This is an int with a user ID value
type.

NamedType works better, though.

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