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§tuple<A...>(values A)

tuple -- feature used to define tuple types

tuple types provide algebraic product types of all the generic arguments
provided to tuple.

The values within a tuple 'tuple<A, B, C>' can be accessed via the tuple's
argument field 'values' followed by a selector referring to the generic
argument's position: 'values.0', 'values.1' and 'values.2', respectively.

Syntactic sugar of the Fuzion language permits an alternative notation
to create values of tuple types as follows

t := (a, b, c, ... )

is equivalent to

t := tuple(a, b, c, ... )

The actual generic types are inferred from the static types of the values
'a', 'b', 'c', ... the tuple is created from.

Similarly, syntactic sugar for the destructuring of tuples can be used
to access the values as in

(a, b, c, ...) := t

In destructurings, we can denote values we are not interested in using
'_' as in

(_, b) := ("first", "second")

which will set 'b' to '"second"' and drop the first element of the tuple.

As an example, say we want to identify a person by its name and its age,
so we can define

a := ("Alice" , 11)
b := ("Bob" , 22)
c := ("Claire", 33)

Then, we could extract Bob's age using

(_, age) := b

or Claire's name using

(name, _) := c

Destructuring also works for general features, e.g.

point (x,y i32) is {}

p := point 3, 4
(px, py) := p # will set px to 3 and py to 4

and the destructured value can then be used to create a tuple

t := (px, py) # will create tuple<i32,i32> instance

however, tuples are not assignment compatible with general features even
if they would destructure into the same types, i.e.,

u tuple<i32, i32> = p # will cause compile time error
q point = (7, 12) # will cause compile time error

The unit tuple '()' can be used as a short-hand to create the empty tuple
'tuple<>()'. The empty tuple can be destructured like any other tuple

() := ()

even though this has no effect.

An instance of the single tuple 'tuple<A>(a)' can not be created using
syntactic sugar '(a)', this will produce the plain value of 'a' instead.
However, destructuring of a single tuple is possible:

(a0) := tuple<A>(a)

which is equivalent to

a0 := a

NYI: A single tuple 'tuple<A>' is currently not assignment compatible with
type 'A', which would make handling of general tuples easier.

tuples and destructuring can be used to swap two elements or create a
permutation as in

(a, b) := (b, a)
(o, t, a, n) := (n, a, t, o)

A tuple type with no actual generic arguments is isomorphic to 'unit', i.e, it
is a type that has only one single value: '()'.