What does scala reflection API Type.dealias do?

Question

I have a simple code,

case class Person(name: String, age:Int)
import scala.reflect.runtime.universe._
val t1 = typeOf[Person]
val t2 = t1.dealias
println(t1 == t2)

It outputs true, so I want to ask what is Type.dealias used for? When should I use it? Some code example would be helpful

I ask so because when I read spark code, ScalaReflection, it almost always use dealias before using the type

Alexey Romanov · Accepted Answer · 2018-07-03T07:43:57.770

5

Type aliases look like

type Alias = Person

It declares a new type Alias which is the same as Person.

dealias resolves these aliases, so that typeOf[Alias].dealias will return typeOf[Person]. Because Person isn't an alias, typeOf[Person].dealias does nothing.

Also note:

Type Equality can be checked with =:=. It's important to note that == should not be used to compare types for equality-- == can't check for type equality in the presence of type aliases, while =:= can.

edited Jul 03 '18 at 07:43

answered Jul 03 '18 at 07:37

Alexey Romanov

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Thanks @alexey-romanov. But there is compiling error for `typeOf[Alias]`, it complains that there is no TypeTag available for Alias – Tom Jul 03 '18 at 07:47
What Scala version are you using? – Alexey Romanov Jul 03 '18 at 08:27
In the command line, it works for me now, both 2.11.8 and 2.12.2.But it doesn't in my Inteillj Idea.. – Tom Jul 03 '18 at 09:00

What does scala reflection API Type.dealias do?

1 Answers1