Fsharp: tuple

By Xah Lee. Date: . Last updated: .

originally ai generated

What is tuple

A tuple is

Tuple is useful for:

Reference tuple and struct tuple

there are 2 types of tuple in fsharp. reference tuple and struct tuple.

normally, it means reference tuple.

Creating tuples

// Tuple of two integers
let xx = (10, 20)
printfn "%A" xx
// (10, 20)
// Tuple with mixed types
let xx = ("Alice", 30, true)  // string * int * bool
printfn "%A" xx
// ("Alice", 30, true)

// Nested tuple
let xx = ((1, 2), (3, 4))
printfn "%A" xx
// ((1, 2), (3, 4))

Accessing tuple elements

let xx = (10, 20)
let x, y = xx
printfn "%d %d" x y
// 10 20

let xx = ("Alice", 30, true)
let name, age, isActive = xx
printfn "%s is %d years old" name age
// Alice is 30 years old

Pattern matching

let xx = (3,4)

// pattern match to get tuple items
match xx with | (a, b) -> printfn "%A %A" a b
// 3 4

Using fst and snd (only for 2-tuple)

// Using fst and snd (only for 2-tuple)
let xx = (10, 20)
let x = fst xx
let y = snd xx
printfn "%d" x
// 10
printfn "%d" y
// 20

note, there's no builtin function for third, etc.

Common operations

// Swap elements

let xx = (10, 20)

// define a swap function
let swap (a, b) = (b, a)

printfn "%A" (swap xx)
// (20, 10)
// Return multiple values from a function
let divide x y =
    if y = 0 then None
    else Some (x / y, x % y)  // tuple inside Option

// Tuple as function parameter
// let add (a, b) = a + b

Struct tuple

there is also a “struct tuple” 

// normal tuple
let xx = (123, "abc")

// type is
printfn "%A" (xx.GetType())
// System.Tuple`2[System.Int32,System.String]

(* The 2 means the arity of the tuple. *)

// compare self
printfn "%b" (obj.ReferenceEquals(xx, xx))
// true

// s------------------------------

// struct tuple
let yy = struct (123, "abc")

// type is
printfn "%A" (yy.GetType())
// System.ValueTuple`2[System.Int32,System.String]

// compare self
printfn "%b" (obj.ReferenceEquals(yy, yy))
// false

Reference