Pfthb

I've just found that Set of type MKAnnotation doesn't work as expected.

class MyAnnotation: MKPointAnnotation 
 let id: String

 init(_ id: String) 
 self.id = id
 

 override var hash: Int 
 return id.hash
 

 static func ==(lhs: MyAnnotation, rhs: MyAnnotation) -> Bool 
 return lhs.hashValue == rhs.hashValue
 


let m1 = MyAnnotation("1")
let m2 = MyAnnotation("2")
let n1 = MyAnnotation("1")
let n2 = MyAnnotation("2")

m1.hashValue //918
n1.hashValue //918

m2.hashValue //921
n2.hashValue //921

if m1 == n1 && m2 == n2 
 print(true)

// prints true

let s1 = Set(arrayLiteral: m1, m2)
let s2 = Set(arrayLiteral: n1, n2)

let i = s1.intersection(s2)
// empty

Intersection of m's and n's is empty even so hashes are the same. Please, compare with example below:

class MyAnnotation: Hashable, Equatable 
 let id: String

 init(_ id: String) 
 self.id = id
 

 var hashValue: Int 
 return id.hash
 

 static func ==(lhs: MyAnnotation, rhs: MyAnnotation) -> Bool 
 return lhs.hashValue == rhs.hashValue
 


let m1 = MyAnnotation("1")
let m2 = MyAnnotation("2")
let n1 = MyAnnotation("1")
let n2 = MyAnnotation("2")

m1.hashValue //918
n1.hashValue //918

m2.hashValue //921
n2.hashValue //921

if m1 == n1 && m2 == n2 
 print(true)

// prints true

let s1 = Set(arrayLiteral: m1, m2)
let s2 = Set(arrayLiteral: n1, n2)

let i = s1.intersection(s2)
// id "1", id "2"

Intersection of m's and n's is as expected.

Isn't it weird? Maybe there is something in the middle I don't know nor understand.

Xcode 10.1

In first code, you haven't use Equatable protocol but in second code you have used Equatable protocol so it is working.

Equatable protocol is used for comparison. You can refer below link for more information:

https://useyourloaf.com/blog/swift-equatable-and-comparable/

The solution is to override isEqual(_ object: Any?) -> Bool.

Because MKAnnotation is derived from NSObject we need to override NS's method. If we dig into implementation (^ + ⌘) we would find:

Subclasses of NSObject can customize Equatable conformance by overriding isEqual(_:). If two objects are equal, they must have the same hash value, so if you override isEqual(_:), make sure you also override the hash property.