apply/get methods in Scala

() implies apply(),

Array example,

scala> val data = Array(1, 1, 2, 3, 5, 8) data: Array[Int] = Array(1, 1, 2, 3, 5, 8) scala> data.apply(0) res0: Int = 1 scala> data(0) res1: Int = 1 

not releated but alternative is to use safer method which is lift

scala> data.lift(0) res4: Option[Int] = Some(1) scala> data.lift(100) res5: Option[Int] = None 

**Note: ** scala.Array can be mutated,

scala> data(0) = 100 scala> data res7: Array[Int] = Array(100, 1, 2, 3, 5, 8) 

In this you can not use apply, think of apply as a getter not mutator,

scala> data.apply(0) = 100 <console>:13: error: missing argument list for method apply in class Array Unapplied methods are only converted to functions when a function type is expected. You can make this conversion explicit by writing `apply _` or `apply(_)` instead of `apply`. data.apply(0) = 100 ^ 

You better use .update if you want to mutate,

scala> data.update(0, 200) scala> data res11: Array[Int] = Array(200, 1, 2, 3, 5, 8) 

User defined apply method,

scala> object Test { | | case class User(name: String, password: String) | | object User { | def apply(): User = User("updupd", "password") | } | | } defined object Test scala> Test.User() res2: Test.User = User(updupd,password) 

If you add an apply method to an object, you can apply that object (like you can apply functions).

The way to do that it is just apply the object as if it was a function, directly with (), without a "dot".

val array:Array[Int] = Array(1,2,3,4) array(0) == array.apply(0) 

For

x(1)=200 

which you mention in the comment, the answer is different. It also gets translated to a method call, but not to apply; instead it's

x.update(1, 200) 

Just like apply, this will work with any type which defines a suitable update method.