What is the syntax behind this statement?

Question

I found this statement:

var o = None: Option[String]

that you can use to set o to a None, with a view to later maybe setting it to a Some[String]

But how does this actual statement break down syntactically? None is an object that extends Option[Nothing] - but how does the rest of the statement work? For example, what does the colon do?

Many thanks!

Answer 1

In scala, you can follow any expression with a type ascription. Like 1: Int is totally valid. So it's really:

var o = (None: Option[String])

The purpose is to tell the compiler that that None should be typed as an Option[String] , so that o isn't typed as None.type . Basically, in this example, it's the same as:

var o: Option[String] = None

More here: https://stackoverflow.com/a/2087356/247985