Enriches union types A | Null
with an interface similar scala.Option making it usable inside for comprehensions
Add the following to your build.sbt
scalacOptions += "-Yexplicit-nulls"
libraryDependencies += "com.abdulradi" %% "nullable-core" % "0.4.0"
import com.abdulradi.nullable.syntax.*
val maybeA: Int | Null = 42
val maybeB: String | Null = "foo"
// Compiles fine
for
a <- maybeA
yield 5
// Also compiles, no null pointer exceptions
for
a <- maybeA
b <- null
yield ()
// Compiles, and evaluates to null (because if condition doesn't match)
for
a <- maybeA
if (a < 0)
yield a
maybeA.map(_ => 5)
maybeA.flatMap(_ => null)
maybeA.flatMap(_ => maybeB)
maybeA.fold(0)(_ + 1)
maybeA.getOrElse(0)
maybeA.contains(0)
maybeA.exists(_ == 0)
maybeA.toRight("Value was null")
val optA = Some(42)
maybeA.toOption == optA
maybeA == optA.orNull
While Option[Option[A]]
is a valid type, the equivalent A | Null | Null
is indistinguishable from A | Null
. So, the library ensures that map and flatMap are used correctly used at compile time.
The following examples don't compile
for a <- maybeA yield maybeB // Shows a compile time error suggesting to use flatMap instead
maybeA.flatMap(_ => 5) // Shows a compile time error suggesting message to use map instead
maybeA.map(_ => null) // Shows a compile time error suggesting to use flatMap instead
maybeA.map(_ => maybeB) // Shows a compile time error suggesting to use flatMap instead
The following doesn't compile, as we can't prove A
won't be Null
def useFlatMapWithNullableInScope[A](f: Int => A): A | Null =
maybeA.flatMap(f)
Solution: Propagate a Nullable instance and let the library check at usage site
def useFlatMapWithNullableInScope[A: Nullable](f: Int => A): A | Null =
maybeA.flatMap(f)
def useMapWithNotNullInScope[A: NotNull](f: Int => A): A | Null =
maybeA.map(f)
If you only care about for-comprehension features, but not the rest of Option-like methods, we also offer a lightweight syntax
import com.abdulradi.nullable.forSyntax.*
for
a <- maybeA
b <- maybeB
res = a + b
if (res % 2) == 0
yield res
The rest of the methods like fold, getOrElse, etc won't be in scope.
Since this library mimics the scala.Option behavior, it made sense to copy and adapt the documentation of it's methods and sometimes the implementation too. Those bits are copyrighted by EPFL and Lightbend under Apache License 2.0, which is the same license as this library.