In scala, check non nullity and apply method directly? - scala

Question

With the following definitions:
class Test {
var activated: Boolean = false
}
def maybeTest(): Test = {
if(...) {
val res = new Test
if(...) res.activated = true
} else null
}
I am having a lot of if structures like this one:
val myobject = maybeTest()
if(myobject != null && myobject.activated) {
// Do something that does not care about the object
}
I would like to condensate it a little bit. Is there a nice way to define/write something like this to avoid a nullPointerException:
if(maybeTest() &&> (_.activated)) {
...
}
What is a best way of achieving this in scala?

Answer 1

You can wrap such code in Option like this:
class Test(num: Int) {
def someNum = num
}
val test: Test = null
Option(test).map(t => t.someNum)
In this example if your variable is null then you will get None, otherwise just work with Some(value)
Update
If you don't want to use Option, then you can define such function
class Test(num: Int) {
def give = num
}
def ifDefAndTrue[T, K](obj: T)(ifTrue: T => Boolean)(then: => K) {
if (obj != null && ifTrue(obj))
then
}
In your case this look like this:
val test = new Test // assuming that activated is false
ifDefAndTrue(test)(_.activate) {
println("results in unit")
}
But it contains side effect and not functional

Answer 2

How about
for {m <- Option(maybeTest())
if m.activated
}
{
... // do something with non-null, activated, m
}

Answer 3

Found the best way with implicit classes, which properly handles the null case (although it might not be the most efficient way).
implicit class CheckNull[T](obj: T) {
def call(f: T => Unit): Unit = if(obj != null) f(obj) else ()
def is(f: T => Boolean): Boolean = if(obj != null) f(obj) else false
}
So I can write a type safe method and even calls:
if(maybeTest() is (_.activated)) {
...
}
myObjectMaybeNull call (_.pause())
Note that parenthesis around (_.activated) are necessary.