4.9. Tuple types

A tuple is a hotch-botch of values. For example, (123, 3.1415) is a tuple, and its type is (int, float).

The tuple type is not a first-class type: it is impossible to declare a variable with a tuple type. A single element tuple type actually is the type of the element. The default value of a tuple type is a tuple with as elements the default values of the tuple type's elements. Tuples can nest: ((1, 2), (3, 4)) is a valid tuple, the type of which is ((int, int), (int, int)). Tuple nesting is rarely used.

The dynamic type can not be an element of a tuple type. All other types are allowed.

The primary use of tuple types is in passing values to or from a method. The following example declares a method divmod which accepts one argument being a tuple of two integers and which returns another tuple of two integers:

<doc> Return (a / b, a % b).  </doc>
(int, int)
  divmod (int, int) (a, b);

Another use of tuples is in shorthands such as simultaneous assignments:

int a, b; ...;
(a, b) = (b, a)

The evaluation of tuple elements is defined to be from left to right. Thus, the result of the following expression

  int i = 0;
  (++i, ++i);

is defined and equal to (1, 2).

The type of an element of a tuple can be neither dynamic nor void.