scalafunctional-programmingscala-option

Is there a scala identity function?

If I have something like a List[Option[A]] and I want to convert this into a List[A], the standard way is to use flatMap:

scala> val l = List(Some("Hello"), None, Some("World"))
l: List[Option[java.lang.String]] = List(Some(Hello), None, Some(World))

scala> l.flatMap( o => o)
res0: List[java.lang.String] = List(Hello, World)

Now o => o is just an identity function. I would have thought there'd be some way to do:

l.flatMap(Identity) //return a List[String]

However, I can't get this to work as you can't generify an object. I tried a few things to no avail; has anyone got something like this to work?

Solution

  • There's an identity function in Predef.

    l flatMap identity[Option[String]]

> List[String] = List(Hello, World)

    A for expresion is nicer, I suppose:

    for(x <- l; y <- x) yield y

    Edit:

    I tried to figure out why the the type parameter (Option[String]) is needed. The problem seems to be the type conversion from Option[T] to Iterable[T].

    If you define the identity function as:

    l.flatMap( x => Option.option2Iterable(identity(x)))

    the type parameter can be omitted.