Embed a value into type with lazy-evaluation in Swift.

lazy_size.swift

import Foundation

protocol Size { static var value: Int { get } }

enum N: Size { static let value = Int(ProcessInfo.processInfo.environment["ARRAY_SIZE_N"]!)! }

zip_array.swift

let a = [0, 1, 2, 3]
let b1 = ["a", "b", "c", "d"]
let b2 = ["a", "b", "c", "d", "e"]

let c1 = Array(zip(a, b1))
print(c1) // [(0, "a"), (1, "b"), (2, "c"), (3, "d")]

let c2 = Array(zip(a, b2))
print(c2) // [(0, "a"), (1, "b"), (2, "c"), (3, "d")]

zip_array_size.swift

protocol Size { static var value: Int { get } }

enum _4: Size { static let value = 4 }
enum _5: Size { static let value = 5 }

struct Array<S: Size, Element> {
    let elements: [Element]

    init?(_ elements: [Element]) {
        guard elements.count == S.value else { return nil }
        self.elements = elements
    }

    init?(_ elements: Element...) {
        self.init(elements)
    }
}

func zip<S: Size, E1, E2>(_ a: Array<S, E1>, _ b: Array<S, E2>) -> Array<S, (E1, E2)> {
    return Array(Swift.Array(zip(a.elements, b.elements)))!
}

let a = Array<_4, Int>(0, 1, 2, 3)!
let b1 = Array<_4, String>("a", "b", "c", "d")!
let b2 = Array<_5, String>("a", "b", "c", "d", "e")!

let c1 = zip(a, b1)
print(c1) // Array<_4, (Int, String)>(elements: [(0, "a"), (1, "b"), (2, "c"), (3, "d")])

// error: cannot convert value of type 'Array<_5, String>' to expected argument type 'Array<_4, String>'
// let c2 = zip(a, b2)