<@U10EJRH2L> Can you construct that type artificially so the compiler is happy?

# announcements

[jlleitschuh]

@Ruckus Can you construct that type artificially so the compiler is happy?

[Ruckus]

What do you mean?

[jlleitschuh]

Is there some way to call validateAndParse without casting fromJson to one specific type?

[jlleitschuh]

Ah, thanks, intersection type was what I needed.
https://stackoverflow.com/a/44453604/3708426

[jlleitschuh]

@Ruckus Apparently JB thinks this is a bug:
https://youtrack.jetbrains.com/issue/KT-7304

[Ruckus]

For intersections, yes. Not for unions.

[jlleitschuh]

What's the difference?

[Ruckus]

Union (commonly represented as A | B) means it can be either A or B. Intersections (commonly represented as A & B) means it has to be both A and B.

[jlleitschuh]

Ah, right.

[Ruckus]

For example (pseudocode):

fun union(x: Int | String) { ... }
fun intersect(x: Int & String) { ... }

union(5)  // OK
union("fred")  // OK
intersect(5)  // ERR: 5 !is String
intersect("fred")  // ERR: "fred" !is Int

[jlleitschuh]

Right, and Kotlin doesn't support union types.
Only intersection types.

[jlleitschuh]

Okay, that makes more sense.

[Ruckus]

Correct

[jlleitschuh]

Thanks!

[Ruckus]

Usually people get around it by creating some sort of wrapper Either<A, B> class (a common idiom in functional programming).

[jlleitschuh]

Yep, big fan of Either types.

[Ruckus]

They can indeed be very nice depending on your style of programming. They can also be a pain if you try to force them into the wrong style.

[Ruckus]

If they work for you though, go for it.