A tuple is a finite ordered list of elements. It is presented as a parentheses-braced, comma-delimited list. In Swift, you can use them as stand-alone heterogenous lists of values or pass them as arguments to functions and closures.

A tuple is pronounced “tupple” (TUH-ple), not “two-pull”. It’s a shortcut pulled from “double, triple, quintuple, sextuple, octuple”, etc. Yes, please note that “quadruple” doesn’t fit with the others and is not used as a basis for speaking the word. Rules about long and short “u”s that apply to other English words are also not relevant to this case.

In Swift, a tuple is analogous to an anonymous struct. Its members are indexed numerically (.0, .1, .2, etc). You can also use labels to access members by name:

let point = (x: 5.0, y: 2.3)
print(point.1) // 2.3
print(point.y) // 2.3

Swift 3.0 and later no longer supports splatting, so you cannot decouple a tuple from a function call. You can read more about this in SE-0029, which disallowed the ability. Before the change, you could call a function either with its direct arguments or by passing a tuple:

func foo(a : Int, b : Int) {}
foo(a: 42, b : 17) // still allowed
let x = (a: 1, b: 2)
foo(x) // no longer allowed in Swift 3+

The continued work on SE-0110 is still resolving on how tuples and closures interact.

The word “arity” describes the number of members in a tuple. (It also describes the number of arguments or operands accepted by a function, method, or closure.) The examples above use an arity of 2. You can call this a “2-arity tuple” or the shortcut “2-ary tuple”. Some shorten that further to a “2-tuple”.  All are acceptable.

Some fun facts to finish with:

• A figurative tuple with an arbitrary arity is an “n-arity” or “n-ary” or “n-tuple”.
• A tuple with a variable number of arguments is variadic.