Think Julia

Chapter 12. Tuples

This chapter presents one more built-in type, the tuple, and then shows how arrays, dictionaries, and tuples work together. It also introduces a useful feature for variable-length argument arrays, the gather and scatter operators.

Tuples Are Immutable

A tuple is a sequence of values. The values can be of any type, and they are indexed by integers, so in that respect tuples are a lot like arrays. The important difference is that tuples are immutable and that each element can have its own type.

Syntactically, a tuple is a comma-separated list of values:

julia> t = 'a', 'b', 'c', 'd', 'e'
('a', 'b', 'c', 'd', 'e')

Although it is not necessary, it is common to enclose tuples in parentheses:

julia> t = ('a', 'b', 'c', 'd', 'e')
('a', 'b', 'c', 'd', 'e')

To create a tuple with a single element, you have to include a final comma:

julia> t1 = ('a',)
('a',)
julia> typeof(t1)
Tuple{Char}

A value in parentheses without comma is not a tuple:

julia> t2 = ('a')
'a': ASCII/Unicode U+0061 (category Ll: Letter,
  lowercase)
julia> typeof(t2)
Char

Another way to create a tuple is using the built-in function tuple. With no argument, it creates an empty tuple:

julia> tuple()
()

If multiple arguments are provided, the result is a tuple with the given arguments:

julia> t3 = tuple(1, 'a', pi)
(1, 'a', π = 3.1415926535897...)

Because tuple is the name of a built-in function, you should avoid using it as a variable name.

Most array operators also work on tuples. The bracket operator ...