I'm sure this is old news and a sign of how little...

# getting-started

[Rob Elliot]

I'm sure this is old news and a sign of how little I read, but...

I've often found myself hankering for the ability to declare a type I don't own implements an interface the way you can in Haskell - I just had a revelation that of course you can:

package module1

data class Thing1(val name: String)

package module2

interface Named {
  val name: String
}

fun Thing1.asNamed() = object : Named {
  override val name: String = <mailto:[e-mail]|[e-mail]>
}

[Rob Elliot]

Does this seem wise? First thing that strikes me is that the anonymous object's equals, hashCode and toString are not going to be nice...

[Jeff Lockhart]

equals, hashCode and toString are not going to be nice

You could overcome this with a class like this one I use in my KMP library to wrap platform implementations. It also has an actual property to access the wrapped object directly.

[Rob Elliot]

Good idea, that’s nice

[Jeff Lockhart]

I also have one that wraps Objective-C `NSObject`s for Kotlin/Native as well. I'm using a similar concept, just with expect/actual classes rather than interfaces.

[Youssef Shoaib [MOD]]

If you control the interface, you can actually do a typeclass-esque pattern with contexts:

interface Summable<T> {
operator fun T.plus(other: T): T
}
object IntSummable: Summable<Int> { ... }
context(Summable<T>) fun List<T>.sum() = ...
// Usage
with(IntSummable) { myList.sum() }