What is type of a singleton?

When I define a singleton in Scala:

object MySingleton{}

then what is the type of this singleton?

The type will be the (here slightly useless) “singleton type” called MySingleton.type.

In general any stable path (val, object, or combinations thereof) has a corresponding singleton type that can be retrieved in a similar way.

1 Like

You can ask the typechecker:

$ scala
Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 9.0.1).
Type in expressions for evaluation. Or try :help.

scala> object S {}
defined object S

scala> val s: Int = S
<console>:12: error: type mismatch;
 found   : S.type
 required: Int
       val s: Int = S


$ scala
scala> :type object S
1 Like