Tuples?

The syntax for creating tuple types is defined as:

'(' type (',' tuple)* ')'

In order to create an instance of a tuple we need only separate the individual tuple values with a comma, the syntax being:

expression (',' expression)+

The maximum number of elements within a tuple is 24.

Tuples are an excellent tool for working with collections of typed data, whilst avoiding the need to define a container class specifically to hold it, or by having to use a list. For example:

ageAndName (int, String) = 24, "dave" //a tuple definition
ageAndNameAlt Tuple2<int, String> = 24, "dave" //a tuple definition with alternative mechanism for declaring tuple type
ageAndName2 = 67, "mary" //tuple type is inferred to be (int, String)

Without tuples, the above would have to be captured in the following ways (amongst others):

class AgeAndNameHolder(-age int, -name String)//using a holder object
ageAndName = new AgeAndNameHolder(24, "dave")

ageAndName2 = [67, "mary"] //holding the data within a list

The holder object can become a very heavy weight pattern to use in code, especially for cases where the data lifetime or manipulation context is very short (contained within a method for instance). Likewise, the list pattern is inconvenient as we must remember to explicitly cast got values and it's mutable, meaning the contents can be accidentally changed. Tuples provide a nice middle ground between the two, as much type safety as classes, but with as much convenience in defining as lists.

A nice advantage of tuples is that they are naturally immutable - once created they cannot be changed (note that the objects they contain, if not immutable can be changed).

Tuples are often used for returning multiple values to or from a function or method invocation:

def getAgeAndName(){
  return 12, "dave"
}

def getAgeAndName2() (int, String) {//with explicit return type definition
  return 12, "dave"
}

Tuples are often used to return multiple values from functions as illustrated in the getAgeAndName2 function above.

Tuple decomposition?

We can extract values from tuples in one of two ways. We can explicitly refer to the field being extracted:

x = 12, 14
e1 = x.f0
e2 = x.f1

Or we can use a decomposition assignment:

x = 12, 14
(e1, e2) = x

If only certain values need to be extracted this can be achieved by simply following the space to ignore with a comma:

x = 12, 14, 15
(e1, , e3) = x

//e1 == 12
//e3 == 15

We can make use of the decomposition assignment within for loops like so:

toSum = [(1, 2), (3, 4), (5, 6)]

for((a, b) in toSum ) { a + b }
//== [3, 7, 11]

This same effect can be achieved within list comprehensions of tuples:

toSum = [(1, 2), (3, 4), (5, 6)]

(a+b) for (a, b) in toSum 
//== [3, 7, 11]

Iterating over Tuples?

Tuples support iteration (i.e. can be used in for loops etc):

x = 12, 13
combined = "" + ("el: " + e for e in x)

//combined == "el: 12 el: 13"

Tuples are Reified Types?

Tuples are reified types, which means that the following is perfectly valid code:

def extractAgeIfNameAndAge(an Object){
  if(an is (int, String)){
    (age,) = an
    age
  }
  -1
}

Tuples in multiple assignment?

Tuples can be used in multiple assignment statements, e.g:

(a, b) = (c, d) = 1, 2

//a == 1
//b == 2
//c == 1
//d == 2

Tuples in typedefs?

Tuples can be used in typedef statements. E.g.

typedef tuple3 = (int, String, double)
typedef myTuple2<x> = (int, x)//with one parameter: x