CODEWITHSUNDEEP
scala
WeiOnThePike
WeiOnThePike

Reputation: 81

How to understand this two lines of scala code?

Stumbled these two lines of code while reading through akka-actor source:

abstract class ExtensionKey[T <: Extension](implicit m: ClassTag[T]) extends ExtensionId[T] with ExtensionIdProvider {
    def this(clazz: Class[T]) = this()(ClassTag(clazz))

At the bottom of this file:

https://github.com/akka/akka/blob/master/akka-actor/src/main/scala/akka/actor/Extension.scala

I cannot wrap my head around the constructor call "this()". No where a constructor is defined without parameters? How does this work? Read a few articles about scala constructor overloads and still can't explain it.

Upvotes: 1

Views: 58

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170713

The primary constructor ExtensionKey[T <: Extension](implicit m: ClassTag[T]) actually has two parameter lists: the first one, for non-implicit parameters, is empty. I.e. this is exactly the same as if they wrote ExtensionKey[T <: Extension]()(implicit m: ClassTag[T]).

Upvotes: 2

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