Couple of `value class` queries :thread:

# getting-started

[Jonathan Mew]

Couple of value class queries 🧵

[Jonathan Mew]

We currently have some "Microtype" classes which wrap a single value. So for example we have a StringMicrotype abstract class extended by a bunch of others. I was exploring the possibility of migrating to inline/value classes instead.

[Jonathan Mew]

I've hit 2 issues so far:
• We have some string types we effectively would like to be case-insensitive. I think I'd need to do something like call a companion MyCaseInsensitiveString.new(s) and pass the lowercased string to a private constructor to preserve that logic.
• We have Exposed Column Types related to our Microtypes - so we have an abstract class StringMicrotypeColumnType<T: StringMicrotype> extended by a few others, each associated with the relevant Microtype (e.g. EmailColumnType associated with Email). Is there a way to use generics to refer to "any value class that contains a String value"?

[Jonathan Mew]

Perhaps these types are legitimately better as non-value classes - I'm not bothered about improving performance, just thought it might mean less/more concise code.

[Jonathan Mew]

@JvmInline
value class EmailAddress private constructor(val value: String) {
    companion object {
        fun new(value: String): EmailAddress = EmailAddress(value.lowercase())
    }
}

[Jonathan Mew]

(the microtypes are pretty concise already - this would mainly just cut out some class hierarchy)

[Stephan Schroeder]

• I like your value class with factory method 👍
• I'm fairly certain that there's no way to use generics to accept any value class containing a String (since this is basically the opposite of what you'd normally want @JvmInline value classes for: more type-safety)
But you could maybe implement an Interface on your value classes and use that!?

interface StringContainer {
  fun getContent(): String
}

[Jonathan Mew]

looks like I might get away with

interface StringContainer {
  val value: String
}

@JvmInline
value class EmailAddress private constructor(override val value: String): StringContainer {
...
}

Not sure it's worth it though 🤔

Thanks for the input!