However, I still cannot get that example to compil...

# announcements

[natpryce]

However, I still cannot get that example to compile when converted to Kotlin syntax. Seems to be a limitation of either the Kotlin type inference algorithm, or (more likely) my ability to bend it to my will.

[Jeremy]

Sovled this problem. thank you!
https://pl.kotl.in/rJIgyjMUE

[natpryce]

Ah yes! Extension functions. Whenever I have a problem wrangling generic type parameters of methods, the problem goes away when I replace methods with functions.

[natpryce]

I must remember that!

[Robert Jaros]

I'm not sure it's ok

[Robert Jaros]

val v = Option("test")
println(v.getOrElse { 0 })

[Robert Jaros]

it should not work this way

[natpryce]

What’s wrong with that?

[natpryce]

I noticed that I solved this very problem with the same solution: https://github.com/npryce/result4k/blob/master/src/main/kotlin/com/natpryce/result.kt#L69

[Robert Jaros]

Option<String> should not return Int

[natpryce]

Option("test").getOrElse{0} has type Any, and println can be passed an Any

[natpryce]

That is… Any is a supertype of String, 0 is an Int, which is a subtype of Any, so B gets unified to Any

[PHondogo]

@Robert Jaros right - with extension function in this case we cannot achive that level of 'type safety'. As i know, there is plan to add lower bound check in 'where' clause...

[Robert Jaros]

I was convinced that Scala's type system is better than Kotlin, but Scala's Option implementation isn't better when it comes to type safety 😉

[Robert Jaros]

scala> Option[java.util.Date](new java.util.Date()).getOrElse(0).getTime()
<console>:8: error: value getTime is not a member of Any

[PHondogo]

Without lower bounds in generic parameters in 'where' it is impossible for now to make perfect solution. Waiting for language improvements...

[Pavlo Liapota]

But what is the problem?
You want that return type is super type of type T. Any is super type of String, so function can return value of type Any and value 0 passes this condition.

I suppose that you agree that this code should be allowed:

Option("test").getOrElse { 0 as Any }

and compiler is just smart enough to infer type which will pass condition even without explicit cast.

[PHondogo]

Generics are invented to avoid this :)