The Scala collections all define the find function. The find operation traverses a collection and returns the first item in the collection that meets the given condition(s).
Perhaps you are a teacher. You have a type that represents a student with a name and a grade:
case class Student(name: String, grade: Int)
And you have a randomized list of those students:
val students = List(
Student("Sally", 79),
Student("Giedrius", 81),
Student("Aryana", 98),
Student("Ty", 94),
Student("Eloise", 86),
Student("Vergil", 89),
Student("Doug", 66),
Student("Delmar", 77),
Student("Makenna", 88),
Student("Orval", 93) )
Maybe you want to reward a random A-student (i.e., a student with a grade of 90 or above) with a candy bar. You can use find to return the first A-student in the list:
val scholar = students.find(_.grade >= 90) // scholar: Option[Student] = // Some(Student(Aryana,98))
So, that’s great: Aryana gets a Twix! (It is the only one with the cookie crunch, after all.)
Notice, by the way, that scholar is not a Student, but rather an Option that contains a Student. Let’s get back to that in a minute.
You also happen to be one of those sadistic teachers, though, who likes to embarrass the students who are not living up to their potential. Therefore you pick a random F-student (i.e., with a grade less than 65) and outfit him/her with a dunce cap:
val dunce = students.find(_.grade < 65) // dunce: Option[Student] = None
Isn’t that interesting? There are no F-students. (Who’s the dunce now?)
That’s the beauty of find: it returns an Option instead of the bare Student. Therefore if no item in the list meets find’s predicate, it does not throw an exception or return null (the way some other languages do). It just returns None. That way, if you write something like this in which you specify that you expect the Student type, Scala does not let you get away with it:
val dunce: Student = students.find(_.grade < 65) // error: type mismatch; // found : Option[Student] // required: Student // val dunce: Student = students.find(_.grade < 65) // ^
It warns you at compile time that you are aiming a firearm at your foot instead of letting you shoot it off at run time with one exception or another.
It could be that you give a test next week that slays the entire class: you may not have an A-student that week. The Option value that find returns makes you test dunce and scholar before you use them to make sure someone is supposed to get a candy bar or a dunce cap before you start handing them out.