Access a tuple's values with a variable

Question

How can I read an item from a tuple based on a dynamic value? For example, if I want "banana" here I do this:

var tuple = ("banana", "sock", "shoe")
print(tuple.0)

But how can I use a value stored in another variable?

var parameter = 0

print(tuple.parameter)

Answer 1

Tuples aren't flexible enough to do this. You can come close with functions:

let tuple = ("banana", "sock", "shoe")

let first = { (t: (String, String, String)) -> String in t.0 }
let second = { (t: (String, String, String)) -> String in t.1 }
let third = { (t: (String, String, String)) -> String in t.2 }

let choice = first
print(first(tuple))

But this isn't scalable at all; you need a set of functions like this for every tuple type you want to interact with.

One option might be to create a struct as an alternative to your tuple. Then you can use a KeyPath. For example:

struct Items
{
    let first: String
    let second: String
    let third: String

    init(tuple: (String, String, String))
    {
        self.first = tuple.0
        self.second = tuple.1
        self.third = tuple.2
    }
}

let choice = \Items.first

let items = Items(tuple: tuple)
print(items[keyPath: choice])

Or, if your tuples are all homogenous like your example, another option is to convert to an array and use array subscripting:

extension Array where Element == String
{
    init(_ tuple: (String, String, String))
    {
        self.init([tuple.0, tuple.1, tuple.2])
    }
}

let array = Array(tuple)
let index = 0
print(array[index])

(Subscript-like keypaths are also coming in future Swift, but they don't buy you anything in this case above a regular subscript.)