Unboxed wrapper types (newtypes)

[lpil]

Support creation of type wrappers that function like custom types of a single field, require explicit boxing and unboxing, and at runtime all boxing is erased so there is no runtime overhead.

i.e. Cents wraps an Int. At runtime it is just an Int, no record wrapper.

This is called a newtype in Haskell.

What should the syntax be?

[CrowdHailer]

Can it using the existing syntax but just be an optimisation on single value types.

e.g.

type Cent{
  Cent(Int)
}

Because there is only ever one variant is there a reason this needs to produce the tuple {:cent, int} it should never be matched on. I think?

Otherwise I would expect something like

type Cent = Int

But I think that is already used for type aliases.

[lpil]

That is the approach that OCaml takes but at the moment I would like to have consistency in the code generation in order to make Erlang FFI more straightforward and to have fewer exceptions to the rules of the language.

At the very least I would like to see what syntax ideas we can come up with.

type Cent = Int

What would the syntax be for boxing and unboxing the newtype in this case? It seems there is no constructor?

[CrowdHailer]

I guess construction makes sense if it looks like

let cents = Cent(5)
let Cent(number) = cents

Perhaps that suggests a syntax of

type Cent(Int)

Questions is there interest in a type that at runtime just puts values in a tuple.
i.e. type Coordinate(x: Int, y: Int) makes {x, y}

Such a thing might be useful for how erlang sometimes represents times or ip addresses.

In which case type Cent(Int) I would expect to make a one element tuple. 🤔

[lpil]

I don't plan to have the ability to construct records without a tag. If this is desired it can be achieved using a newtype over a tuple.

I don't think the syntaxes above fit the Gleam pattern of type TYPE_NAME VALUE_CONSTRUCTORS. Will have to give this more thought.

[eterps]

i.e. Cents wraps an Int. At runtime it is just an Int, no record wrapper.

In Nim that would be type Cent = distinct Int

[lpil]

ooh thanks! I had not looked at Nim

[eterps]

Nim's way to construct such a value also makes me think of the units of measure notation in F# but that's a completely different feature.

[lpil]

Wow, that's amazing. F# has so much interesting stuff in it, I need to learn it!

[eterps]

Wow, that's amazing. F# has so much interesting stuff in it, I need to learn it!

In that case I'd recommend reading this book, it gives a good idea what Gleam can be for the BEAM ecosystem in very practical terms.

[lpil]

Oh dear, my just as I thought I was starting to get through books faster than I collected them 😆

Thanks for the recommendation, it sounds great

[lpil]

Just ordered a copy! :)