CODEWITHSUNDEEP
scala
Kevin Meredith
Kevin Meredith

Reputation: 41909

Print Type Parameter's Type

Given:

scala> def f[A]: Unit = ???
f: [A]=> Unit

I'd like to replace the definition to print out A's type.

Is there any alternative to:

scala> def f[A](implicit manifest: scala.reflect.Manifest[A]) = manifest.toString
f: [A](implicit manifest: scala.reflect.Manifest[A])String

scala> f[String]
res10: String = java.lang.String

Upvotes: 3

Views: 1823

Answers (1)

Michael Zajac
Michael Zajac

Reputation: 55569

That isn't actually printing out the type, it's printing out the class.

scala> f[List[Int]]
res17: String = scala.collection.immutable.List[Int]

Use a TypeTag to get the type information. But no, there isn't a simpler way. Since this is happening at runtime, you need the TypeTag to hold the type information.

scala> import scala.reflect.runtime.universe.{TypeTag, typeOf}
import scala.reflect.runtime.universe.{TypeTag, typeOf}

scala> def f[A](implicit tt: TypeTag[A]): Unit = println(typeOf[A])
f: [A](implicit tt: reflect.runtime.universe.TypeTag[A])Unit

scala> f[List[Int]]
scala.List[Int]

We can make it look more concise with the context bound syntax:

def f[A : TypeTag]: Unit = println(typeOf[A])

Upvotes: 12

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