Tuples in F#

Tuples are collections where each element can be of different type. If you have a C# or Python background then you must be familiar with tuples. A tuple can be used to return multiple values from a function without having to declare an object for it.

Here’s a tuple with 5 elements:

let addThreeNumbers x y z = x + y + z
let myFirstTuple = (45, "hello world", 5., true, addThreeNumbers)

This tuple has an integer, a string, a float, a boolean and a function in it.

val myFirstTuple : int * string * float * bool * (int -> int -> int -> int) = (45, “hello world”, 5.0, true, )

There’s no index-based way to access a specific element in the tuple. We can get to the elements by naming them as follows:

let myFirstTuple = (45, "hello world", 5., true, addThreeNumbers)
let (myInt, myString, myFloat, myBool, myFunc) = myFirstTuple
printfn "Integer in the tuple: %i" myInt
let myFuncRes = myFunc 1 2 3

The variables declared in (myInt, myString, myFloat, myBool, myFunc) will get the respective values in the tuple:

val myString : string = “hello world”
val myInt : int = 45
val myFunc : (int -> int -> int -> int)
val myFloat : float = 5.0
val myBool : bool = true
val myFuncRes : int = 6

For tuples with 2 elements the special functions fst and snd – first and second – are used to access the elements:

let tupleDouble = ("hello world", true)
let greeting = fst tupleDouble
let lovesMeLovesMeNot = snd tupleDouble

val tupleDouble : string * bool = (“hello world”, true)
val greeting : string = “hello world”
val lovesMeLovesMeNot : bool = true

View all F# related articles here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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