7.5. Tuple

A tuple is a way of grouping multiple values with potentially different types into one type. All types may be stored within tuples except streams and other tuples.

7.5.1. Declaration

A tuple value is declared with the keyword tuple followed by a parentheses-surrounded, comma-separated list of types. The list must contain at least two types. Tuples are mutable. For example:

tuple(integer, real, integer[10]) t1;
tuple(character, real, string[256], real) t2;

The fields of a tuple may also be named. For example:

tuple(integer, real r, integer[10]) t3;
tuple(character mode, real, string[256] id, real) t4;

Here, t3 has a named real field named r and t4 has a named character field named mode and another named string field named id.

The number of fields in a tuple must be known at compile time. The only exception is when a variable is declared without a type using var or const. In this case, the variable must be initialised immediately with a literal whose type is known at compile time.

7.5.2. Access

The elements in a tuple are accessed using dot notation. Dot notation can only be applied to tuple variables and not tuple literals. Therefore, dot notation is an identifier followed by a period and then either a literal integer or a field name. Spaces are not allowed inbetween elements in dot notation. Field indices start at one, not zero. For example:

t1.1
t2.4
t3.r
t4.mode

Tuple access can both be used to retrieve the element value for an expression as well as to assign a new value to the element.

y = x + t1.1;     // Allowed
t1.1 = type-expr; // Allowed

7.5.3. Null

null is every field assigned their type-appropriate null for tuple.

7.5.4. Identity

identity is every field assigned their type-appropriate identity for tuple.

7.5.5. Literals

A tuple literal is constructed by grouping values together between parentheses in a comma separated list. For example:

tuple(integer, string[5], integer[3])  my_tuple = (x, "hello", [1, 2, 3]);
var my_tuple = (x, "hello", [1, 2, 3]);
const my_tuple = (x, "hello", [1, 2, 3]);
tuple(integer, real r, integer[10]) tuple_var = (1, 2.1, [i in 1..10 | i]);

7.5.6. Operations

The following operations are defined on tuple values. In all of the usage examples tuple-expr means some tuple yielding expression, while int_lit is an integer literal as defined in Integer Literals and id is an identifier as defined in Identifiers.

Class	Operation	Symbol	Usage	Associativity
Access	dot	`.`	`tuple-expr.int_lit` `tuple-expr.id`	left

Comparison	equals	`==`	`tuple-expr == tuple-expr`	left
	not equals	`!=`	`tuple-expr != tuple-expr`	left

Note that in the above table tuple-expr may refer to only a variable for access. Accessing a literal could be replaced immediately with the scalar inside the tuple literal. However tuple-expr may refer to a literal in comparison operations to enable shorthand like this:

if ((a, b) == (c, d)) { }

Comparisons are performed pairwise, therefore only tuple values of the same type can be compared. This table describes how the comparisons are completed, where t1 and t2 are tuple yielding expressions including literals:

Operation	Meaning
`t1 == t2`	`t1.1 == t2.1 and ... and t1.n == t2.n`
`t1 != t2`	`t1.1 != t2.1 or ... or t1.n != t2.n`

7.5.7. Type Casting and Type Promotion

To see the types that tuple may be cast and/or promoted to, see the sections on Type Casting and Type Promotion respectively.