Groovy Tuples

A tuple is an ordered, immutable list of elements. 

Groovy has it's own groovy.lang.Tuple class.

 We can create an instance of a Tuple by providing all elements that need to be in the Tuple via the constructor. 

We cannot add new elements to a Tuple instance or remove elements. 

We cannot even change elements in a tuple, so it is completely immutable.

 This makes it very useable as return value for a method where we need to return multiple values. 

Groovy also provides a Tuple2 class that can be used for tuple instance of only two elements. The elements are typed in a Tuple2 instance.


def tuple = new Tuple('one', 1, new Expando(number: 1))
 
assert tuple.size() == 3
 
// To get the value of an element
// at a certain position we use
// the get(index) method.
assert tuple.get(0) == 'one'
 
// We can use the [] syntax to
// get elements from the tuple.
assert tuple[1] == 1
 
// We can use methods added to the
// Collection API by Groovy.
assert tuple.last().number == 1
 
// We cannot add the tuple.
try {
    tuple.add('extra')
    assert false
} catch (UnsupportedOperationException e) {
    println e
    assert e
}


// We cannot remove the tuple. 
try {
    tuple.remove('one')
    assert false
} catch (UnsupportedOperationException e) {
     println e
    assert e
}


// We cannot change the tuple. 
try {
    tuple[0] = 'new value'
    assert false
} catch (UnsupportedOperationException e) {
     println e
    assert e
}
 
 
// Create a Tuple with fixed size
// of 2 elements, a pair.
def pair = new Tuple2('two', 2)
 
// The Tuple2 class has extra methods
// getFirst() and getSecond() to
// access the values.
assert pair.first == 'two'
assert pair.second == 2