Importing type variants

[Dan-C-Reed]

I have a file called types.gleam that contains the following:

pub type DataSource {
  Url
  File
}

and I'd like to use it in another file, so I import the DataSource type like so:

import gleam/string
import types.{type DataSource}

pub fn get_source_type(path: String) -> DataSource {
  case string.starts_with(path, "http") {
    True -> Url
    False -> File
  }
}

This throws an error that Url is not in scope despite importing DataSource. I think I must also need to import the Url variant of DataSource, however, I'm not sure how. When the function and the type live in the same file everything is peachy.

Can someone advise me how to import a variant of a type?

[Dan-C-Reed]

Of course, immediately after I post this I figure it out. 🤦‍♂️ I import Url like a function and not a type because it's considered a constructor. So,

import types.{type DataSource, Url, File}

[barcek]

Adding a thought on this subject, re something I've noticed early on using Gleam. Importing a larger number of variants in this way can get unwieldy, especially having to update imports if the custom type is extended or reduced at a later point in development.

Using @Dan-C-Reed's example above, it would be useful if all variants didn't need to be imported, but could be accessed via the type in place, e.g.:

import types.{type DataSource}
...
  True -> DataSource.Url
...

This would help clarify the relationship between variants locally too.

Using the qualified import syntax, i.e. accessing via the module name, is possible and reasonable if there's only one custom type per module, but with multiple types each with multiple variants also potentially confusing.

[barcek]

Didn't spot this was closed, and wouldn't show up in the default listing. Posted with some changes as discussion #3512.