Is there a specific way to use tuples as set elements in Swift?

Question

I want to do set operations on co-ordinate pair elements from an x-y grid.

E.g. {(0,0),(1,4),(1,5),(2,3)} union with {(2,3),(1,4),(2,6)} = {(0,0),(1,4),(1,5),(2,3),(2,6)}

Unfortunately I can't work out a way of inserting tuples into Swift's Set commands as it says that they do not conform to the 'hashable' protocol.

Error: type '(Int, Int)' does not conform to protocol 'Hashable'

I believe I've got a work around but it involves a lot of code. Is there a simple way that I'm missing before I hit the grindstone?

Answer 1

Rather than using tuples to represent points, use the built in type CGPoint. You can extend CGPoint to be hashable by extending it:

import UIKit

extension CGPoint: Hashable {
    public var hashValue: Int {
        return self.x.hashValue << sizeof(CGFloat) ^ self.y.hashValue
    }
}

// Hashable requires Equatable, so define the equality function for CGPoints.
public func ==(lhs: CGPoint, rhs: CGPoint) -> Bool {
    return CGPointEqualToPoint(lhs, rhs)
}

Now that CGPoint is Hashable, you can use it in sets. For example:

let point1 = CGPoint(x: 0, y: 1)
let point2 = CGPoint(x: 0, y: 2)
let point3 = CGPoint(x: 1, y: 1)
let point4 = CGPoint(x: 3, y: 3)
let point5 = CGPoint(x: 3, y: 3)  // Intentionally the same as point4 to see the effect in union and difference.

let set1 = Set([point1, point2 , point5])
let set2 = Set([point4, point3])

let union = set1.union(set2) // -> {{x 0 y 2}, {x 3 y 3}, {x 0 y 1}, {x 1 y 1}}
let difference = set1.intersect(set2) // -> {{x 3 y 3}}