Difference between Tuple and List[Any] in Scala?

Question

Currently, I am learning Scala and reading this book Programming in Scala and which says, " Unlike an array or list, a tuple can hold objects with different types." For example, the following tuple contain Int, String and Float.

val tup = (1, "hello", 4.4)

Again, the book say, "If you want to have any type of element in list/array, then you can use Any Datatype."

val list = List[Any](1, "hello", 4.4)

So, what is the difference between above these 2 approaches? what are the benefit of one over another?

Answer 1

Any is a data-type , just like Int or String, but different from them.
Tuple is a container, which can hold multiple data-types, i.e. it can contain vals of different data-types, but the type of the Tuple will depend upon how many elements are there in the Tuple, so for example:

val tup = (1, "hello", 4.4) // type of tup here is scala.Tuple3 (Int, String, Double)
val tup = (2.3, null) // type of tup here is scala.Tuple2  (Double, Null)
val tup = (5:Any, "hello", 2.2) // type of tup here is scala.Tuple3 (Any, String, Double)

But the type of each of the elements in the Tuple will be maintained. Any on the other hand, is like a homegenous data-type in which there's no unique type identity of the elements, be it a String or Int or Null type initially, will be converted to a single data-type Any and will lose all type-information.

Update:
The difference between a Tuple and a List[Any] is that a Tuple can hold elements of multiple data types, still maintaining the data type of the individual elements.
While a List or Array can only hold elements of a single data type, so a List[Any] will consist of all elements of type Any , so it'll basically convert all the elements (irrespective of their earlier data-type) to Any.

Answer 2

I don't agree with PawelN

val list = List[Any](1, "hello", 4.4)
for (i <- list) println(i.getClass)

or

val array = Array[Any](1, "hello", 4.4)
for (i <- array) println(i.getClass)

results in:

class java.lang.Integer
class java.lang.String
class java.lang.Double

Hence, no casting is needed when you access an item in a List or an Array of Any. Of course, I'd be suspicious of design of code that is using such a thing.

The main point of a Tuple, is for a function to be able to return arbitrary numbers of objects of different types. This is much lighter weight then creating a class every time you need to return multiple values at the cost of some type safety.

Answer 3

tup has type (Int, String, Double), so you can get data back with its correct type: tup._1 has type Int. list has type List[Any], so you've lost all type information: list(0)'s type is Any.

Don't use Any (or List[Any], etc.) unless you have to; certainly don't use it when a tuple will do.

Answer 4

Tuples are type safe and with List[Any] you have to cast element to appropriate type.

val tup = (1, "hello", 4.4)
tup._2 --> gives you string

val list = List[Any](1, "hello", 4.4)
list(1) --> gives you object of type Any and you have to cast this object

Your tuple is a class of type Tuple3[Int, String, Double].